Catch Per Unit Effort Trends Research Articles

Phenotypic plasticity, and temporal and spatial variation in the relative abundance of lentic brook trout, Salvelinus fontinalis, across Ontario.

Brook trout (Salvelinus fontinalis) are a highly prized species found in lakes and streams throughout Ontario. A broadscale monitoring program (BsM) has been conducted in lakes throughout the province, in 5-year cycles, which targets Salvelinus fontinalis populations. The objective of this study was to use the data gained from the BsM and establish a contemporary baseline on the variation of relative abundance and demographics of natural lake populations of S. fontinalis in Ontario. Additionally, given the variability in environmental conditions across the landscape, an objective was to assess the factors, abiotic and biotic, that influence relative abundance among waterbodies. Over the three BsM cycles (2008-2022), 273 S. fontinalis waterbodies were assessed, some multiple times, and 124 were unique populations. S. fontinalis were sampled in 112 of these unique lakes. In total, 7487 S. fontinalis were caught and 5372 were fully sampled (length, weight, and age assessed). The mean catch-per-unit-effort (CPUE) in all waterbodies was 1.4 (0.12 standard error) S. fontinalis per net gang. There was not a significant trend in CPUE over the three BsM cycles nor did CPUE vary significantly among BsM cycles at the provincial scale, but CPUE varied significantly among fisheries management zones (FMZs). Multiple variables were examined to explain the variation in CPUE across the province; a negative association with species diversity was the only variable considered significant. Furthermore, S. fontinalis were more associated with the relative abundance of small cyprinids (i.e., chubs and shiners) and negatively associated with centrarchids, smelt, and other game species. Mean growth potential was greater for males than females but not significantly, whereas longevity favored females. Growth potential and parameters were similar between sexes within FMZs but varied among FMZs. Mean survival among these populations was 25.7%, ranging from 15.2% to 45.6%, with a mean instantaneous mortality of 1.41. This study provided a contemporary assessment of the current range and variability in relative abundance population dynamics of S. fontinalis in lakes within Ontario. This provides a benchmark to assess changes with the pending stressors of climate change and human expansion across the landscape.

Combining catch-based indicators suggests overexploitation and poor status of Indonesia's deep demersal fish stocks

The Indonesian deep-slope demersal fisheries are economically valuable and contribute to the wellbeing of millions of people. However, the sustainability of these fisheries is uncertain because they lack data and assessment. As a precursor to management, we developed and applied a framework for using standardized catch per unit effort (CPUE) and spawning potential ratio (SPR) as indicators to assess eight primary species-fishing gear complexes: the Malabar blood snapper Lutjanus malabaricus (droplines and longlines), goldbanded jobfish Pristipomoides multidens (droplines and longlines), sharptooth jobfish P. typus (droplines and longlines), crimson snapper L. erythropterus (droplines), and rusty jobfish Aphareus rutilans (droplines). We standardized CPUE by identifying relevant fishing trips using a species-association approach and removing any changes in the index not attributable to abundance by using a delta-generalized linear model. SPR values were estimated on a per-recruit basis from life-history parameters using length data. Results indicated that in 2020, all stocks were unhealthy (SPR values < 25%) with only a few exceptions (e.g., P. multidens and L. erythropterus). Most fishing grounds with low SPR values had stable or decreasing CPUE trends, suggesting that current fishing rates are suboptimal or unsustainable. However, L. erythropterus had an increasing CPUE trend but moderate to low SPR, indicating that fishing pressure has decreased so SPR may be an underestimate, leading to an optimistic but uncertain conclusion about stock health and the sustainability of current fishing rates. Such discrepancies between CPUE and SPR may be challenging for the implementation of management measures, but we have outlined and applied a framework for interpretation. The most recent yield values set by the Indonesian Ministry of Marine Affairs and Fisheries for these stocks, however, are 1.4–2.4 times higher than our calculations. This discrepancy may be attributed to several factors, such as inclusion of species that are atypical for deep demersal fish stocks in the Ministry's estimates, differences in methods or the types of data used, or annual variability.

Trends in the abundance of Celtic Sea demersal fish: Identifying the relative importance of fishing and environmental drivers

The Celtic Sea is a productive fishing ground, therefore identifying the relative importance of fishing and environmental factors on fish stock dynamics is crucial for developing our understanding of sustainable yields and to operationalize Ecosystem Based Fisheries Management (EBFM). We investigated the effect of environmental variables and fishing on the relative abundance inferred from catch-per-unit-effort (CPUE), of twelve demersal stocks (i.e., cod, haddock, whiting, anglerfish, hake, megrim, plaice, sole, lesser-spotted dogfish, spurdog, Trisopterus spp., skates and rays) in the Celtic Sea from 1997 to 2019 (23 years). Annualized time series (1997-2019) of net primary production, bottom temperature, copepod abundance (Calanus finmarchicus and Calanus helgolandicus) and North Atlantic Oscillation index were used to characterize key environmental variables. Fishing exploitation rates (F/FMSY) were used to represent fishing pressure and CPUE trends derived from an International Bottom Trawl Survey (IBTS) were used to infer abundance. We used redundancy analysis to identify key explanatory variables and then dynamic factor analysis to assess their relationships with the CPUE series and identify underlying patterns in the unexplained temporal variation. Our results show that for the majority of demersal fish species, the CPUE trends were strongly influenced by fishing exploitation rates. The gradual reduction in exploitation rates observed throughout the study period most likely led to the partial recovery of cod, spurdog, hake, megrim, plaice, whiting, Trisopterus spp., and the skates and rays. In addition, exploitation patterns on one stock influenced CPUE trends of other demersal stocks (e.g., hake, megrim, plaice, lesser-spotted dogfish, sole). We also observed that the CPUE of whiting, hake and plaice increased when C. finmarchicus were abundant in the plankton. We infer from our findings in the investigated time series that the recovery of cod, spurdog, hake, megrim, plaice, whiting, Trisopterus spp., and the skates and rays in the Celtic Sea remains dependent on controlling fishing mortality, and this would not, at least for now, be confounded by the environmental conditions.

Spatial and temporal catch concentrations for Antarctic krill: Implications for fishing performance and precautionary management in the Southern Ocean

The undergoing rapid climate changes recorded along the Western Antarctic Peninsula (WAP) in combination with the increasing seasonal catches reported by the krill fishery have raised concerns as to whether the management strategy established by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is effectively avoiding impacts on the krill stock and related ecosystem.Despite the current fixed catch limit being spread across fishing areas to reduce spatial catches concentrations, our 38-year analysis revealed the highest historical spatial (ton/km2) and temporal (ton/day) fishing concentration levels across the WAP and South Orkney Islands. Higher seasonal catches in recent decades removed persistently within the same small fishing areas and during shorter fishing seasons are key factors influencing this situation.We used the catch per unit effort (CPUE) as a measure of fishing performance. CPUE was standardized using a GAMM model taking into account operational factors such as fleet composition, trawling methods, seasonality and daily catches, and we detected negative CPUE trends over time and across the different fishing areas. Our results suggest that the fishing performance have responded to the elevated spatio-temporal fishing concentration and changes in sea-ice. We discuss whether the negative CPUE trends are caused by fishing-induced depletion or driven by other factors such as krill flux, reduction and contraction of krill abundance and increased cetacean foraging (due recovery of whale populations). Finally, we also highlight the need to expand the survey's coverage (by acoustic or net-based methods) to the new, highly fished, and non-monitored areas such as Gerlache Strait, which is an important area for krill and dependent predators.

Shifts in composition of fish species of fishery in Lake Naivasha, Kenya: Trend implications for fishing effort, yields and revenue

AbstractAssessing fisheries resource composition and exploitation trends is vital for the sustainable management of fish stocks. Accordingly, the present study analysed datasets of fish catches and market values from 1991 to 2019, and from 2004 to 2019, respectively, to determine shifts and trends in fish species composition, fishing effort, fish yield and revenue. The annual percentage weight composition and relative biomass of different fish species in the lake were calculated over the study period. Fishery time series data comprised fishing effort, fish yield, catch per unit effort (CPUE), revenue and revenue per unit effort (RPUE). Moving average (MA) trends at 5‐year intervals were plotted and the Mann–Kendall (MK) method applied to detect trends at the 95% confidence limit. The results identified shifts in fish species composition during various periods, with Nile tilapia Oreochromis niloticus comprising 94% of the total weight of fish landed in 2019, with an overall mean relative biomass of 4221.4 ± 2229.7 kg/km2. The mean total fish catch (1683.5 ± 420 ton/year), CPUE (10.6 ± 2.0 ton/boat/year) and modal effort (176 boats) were highest from 2014 to 2019 period. The fishery revenue increased in 2019 (US$ 4,096,490) with a RPUE of US$ 22,263.5/boat/year. The fishing effort, fish yields, CPUE, revenue and RPUE trends increased significantly (p &lt; .01), likely being related to the shifts in species composition. Lake Naivasha is a learning model for improving fisheries management and yields through stock enhancement interventions. Nevertheless, the increasing level of fishing effort warrants a precautionary approach to ensure sustainability of the fishery resource.

Modeling of Lake Malombe Annual Fish Landings and Catch per Unit Effort (CPUE)

Forecasting, using time series data, has become the most relevant and effective tool for fisheries stock assessment. Autoregressive integrated moving average (ARIMA) modeling has been commonly used to predict the general trend for fish landings with increased reliability and precision. In this paper, ARIMA models were applied to predict Lake Malombe annual fish landings and catch per unit effort (CPUE). The annual fish landings and CPUE trends were first observed and both were non-stationary. The first-order differencing was applied to transform the non-stationary data into stationary. Autocorrelation functions (AC), partial autocorrelation function (PAC), Akaike information criterion (AIC), Bayesian information criterion (BIC), square root of the mean square error (RMSE), the mean absolute error (MAE), percentage standard error of prediction (SEP), average relative variance (ARV), Gaussian maximum likelihood estimation (GMLE) algorithm, efficiency coefficient (E2), coefficient of determination (R2), and persistent index (PI) were estimated, which led to the identification and construction of ARIMA models, suitable in explaining the time series and forecasting. According to the measures of forecasting accuracy, the best forecasting models for fish landings and CPUE were ARIMA (0,1,1) and ARIMA (0,1,0). These models had the lowest values AIC, BIC, RMSE, MAE, SEP, ARV. The models further displayed the highest values of GMLE, PI, R2, and E2. The “auto. arima ()” command in R version 3.6.3 further displayed ARIMA (0,1,1) and ARIMA (0,1,0) as the best. The selected models satisfactorily forecasted the fish landings of 2725.243 metric tons and CPUE of 0.097 kg/h by 2024.

OVERFISHING AND OVERCAPACITY SMALL SCALE FISHERIES IN SEMARANG CITY

Fisheries in Semarang City are dominated by small-scale fisheries. This is indicated by the use of the largest fishing fleet of 10 gross tons operating near the coast. This study aims to analyze the status of small-scale fisheries in Semarang City for sustainable management. Sustainable management is management that guarantees the availability of natural resources and environmental services for future generations. The study was conducted for three months, namely September-November 2018 in the coastal waters of Semarang City, which was part of the Fisheries Management Region (WPP) 712. The method used in this study is the analysis of time series surplus production, namely data from the catch (ton/year) and the number of fishing gear (unit) within 10 years (2007-2016), to calculate the catch per-unit effort (CPUE), maximum sustainable yield (MSY), optimum effort (fopt), utilization rate (TP) and capacity level (TK). This study was obtained results of a downward trend in CPUE; the existing fishery catch or production in 2016 has exceeded the MSY value is 479 tons/year (Schaefer) and 439.11 tons/year (Fox); utilization rate of more than 100% which is 108-127% (Schaefer) and 118-138% (Fox), so that small-scale fisheries in Semarang City are at the level of over-exploited. Based on the fopt analysis, the number of fishing gear used (fexisting) has exceeded the optimum effort with a fishing capacity exceeding 100%, so that small-scale fisheries in Semarang City have experienced overcapacity.

Effects of inconsistent reporting, regulation changes and market demand on abundance indices of sharks caught by pelagic longliners off southern Africa.

The assumption of a proportional relationship between catch-per-unit-effort (CPUE) and the abundance of sharks caught by pelagic longliners is tenuous when based on fisher logbooks that report only retained specimens. Nevertheless, commercial logbooks and landings statistics are often the only data available for stock status assessments. Logbook data collected from local and foreign pelagic longline vessels operating in four areas off southern Africa between 2000 and 2015 were used to construct standardized CPUE indices for blue sharks Prionace glauca and shortfin makos Isurus oxyrinchus. Generalized linear mixed models were used to explore the effects of year, month, vessel, fleet and presence of an observer on blue shark and shortfin mako variability. Landing statistics and auxiliary information on the history of the fishery, regulation changes, and market factors were superimposed on the CPUE indices, to test hypotheses that they would influence CPUE trends. Indices in the West and Southwest (Atlantic) areas were elevated for both species, compared to the South and East (Indian Ocean). The scale of year-on-year CPUE increments, up to an order of magnitude for blue sharks, reflected occasional targeting and retention, interspersed with periods where blue sharks were not caught, or discarded and not reported. Increments were smaller for higher value shortfin makos, suggesting that indices were less affected by unreported discarding. CPUE indices and landings of both shark species have increased in recent years, suggesting increased importance as target species. Analysis of logbook data resulted in unreliable indicators of shark abundance, but when trends were interpreted in conjunction with landings data, disaggregated by area and month, and with hindsight of market demand and regulation changes, anomalies could be explained.

Evaluation of Florida stone crab life history and management scenarios using spawning potential ratios

The stone crab, Menippe mercenaria, supported the third most valuable fishery in Florida in 2016. Declining catch per unit effort (CPUE) and a negative trend in landings since 2000 have raised concerns among fishermen, researchers, and fishery managers as to the fishery’s sustainability. The Fish and Wildlife Research Institute of the Florida Fish and Wildlife Conservation Commission estimates that the state’s stone crab fishery has been overexploited since 1997. This stock status determination, however, is based largely on trends in total landings and CPUE and does not account for the life-history parameters that describe stock productivity, such as size at maturity, fecundity, and survivorship. In this study, an age-structured per-recruit model was developed to evaluate how alternative biological parameters and management scenarios might affect reproductive output, calculated as the spawning potential ratio (SPR), of a theoretical stone crab population. The model incorporated new estimates of size at maturity, fecundity, and temperature-dependent release mortalities. Spawning potential ratios increased with decreasing size at sexual maturity and were sensitive to increasing natural mortality. The largest contributor to changes in SPR was mortality associated with the declawing and release of stone crabs. We also assessed various management scenarios including regulations governing minimum claw length, requiring the use of juvenile trap excluder devices, and institution of temperature-dependent season openings. Increasing the minimum claw length and excluding small juveniles from traps provided moderate protection to the spawning stock. The model suggests that adaptive management strategies that allow fishing only when water temperatures are below 24 °C (the temperature at which modeled survival is improved) could greatly reduce mortality and increase SPR. We examined a suite of management scenarios on the effect of SPR, but additional research should be conducted to determine the socioeconomic impact of changes in regulations in this valuable fishery.

Application of a mixed modelling approach to standardize catch-per-unit-effort data for an abalone dive fishery in Western Victoria, Australia

Despite the prevalence of catch per unit effort (CPUE) as a key metric in fisheries assessments it can be fraught with inherent problems that often cause its use as an index of abundance to become contentious. This is particularly the case with abalone, a sedentary shellfish targeted by commercial dive fishers around the globe. It is common practice to standardize CPUE to at least partly address issues about how well it reflects the actual abundance of a stock. Differences between standardized and unstandardized trends may lead to controversy between scientists and stakeholders when standardized trends provide a less optimistic picture of stock status. It is within this context that we applied Linear Mixed Model (LMM) and Generalized Linear Mixed Model (GLMM) methods to standardize CPUE for the Western Zone blacklip abalone fishery in Victoria, Australia. This fishery was chosen for our evaluation because it included substantial population losses from a disease shock during the middle of the time series. The effects of diver, reef location, month and their interactions with year were included as random effects in these models and the results compared with nominal geometric means. The two standardization methods provided similar standardized CPUE trends and clearly demonstrated that a large proportion of the variance could be attributed to diver and spatial effects. The GLMM seemed to explain more variability in the data and produced better precision for standardized CPUEs than LMM. The temporal trend in variability attributed to divers and spatial scales reveals the impact of disease as well as any homo/heterogeneity effect. The CPUE trends responded to the impact of disease against a backdrop of declining stock, however when compared with the inter-annual pattern in nominal CPUE, the standardized trends showed that the decline immediately following the onset of disease was less precipitous. In contrast to what appeared to be an increase in the nominal series during the more recent post-disease period, there was only a slight non-significant increase observable in the standardized trends.

The effect of hook spacing on longline catch rates: Implications for catch rate standardization

Catch per unit effort (CPUE) is a widely used index of population abundance for informing stock assessments for the purpose of estimating population status and setting fishing policies. However, for CPUE to be an unbiased index, influences that are not related to population abundance (e.g., spatial variation in effort and temporal changes in gear efficiency) must be accounted for in analyses known as CPUE standardization. In longline fisheries, one important factor that can affect CPUE is the spacing between hooks (‘spacing effect’), which influences effective effort and has largely been ignored in previous analyses. Here, we use the Pacific halibut (Hippoglossus stenolepis) long-line fishery as a case study to explore the spacing effect. Both commercial and experimental (fishery-independent) data with hook spacing, and a survey-based CPUE series, are available for this fishery. It thus provides a unique opportunity to explore the effect of hook spacing and its effect on CPUE trends. We quantify this effect using non-parametric and parametric relationships inside a spatially-explicit (geospatial) CPUE standardization model for commercial data, and non-linear mixed-effects model for experimental data. We found a clear non-linear spacing effect (i.e., hooks were less effective the closer they were), but accounting for space had a larger effect on CPUE trends than accounting for hook spacing. For this stock, it is likely the effect of hook spacing on CPUE was minimal due to little variation in average hook spacing over time. Regardless, historical and future trends in hook spacing can have important effects on longline CPUE standardization, highlighting the value of collecting this information. Accounting for hook spacing effects in other fisheries may improve estimates of trends in relative abundance and lead to better management.

Status of the California sea cucumber (Parastichopus californicus) and red sea urchin (Mesocentrotus franciscanus) commercial dive fisheries in the San Juan Islands, Washington State, USA

The San Juan Archipelago is the most intensely fished region of Washington State for echinoderms. Commercial dive fisheries for both the California sea cucumber (Parastichopus californicus) and red sea urchin (Mesocentrotus franciscanus) were characterized by high levels of harvest in the late 1980s and early 1990s. Here we evaluate stock performance of both species under the current fishery management regime using biomass estimates from a remotely-operated vehicle survey, time series of relative abundance from SCUBA index station surveys, and harvester log book data. We also report habitat associations of both species with depth and seafloor substrate composition. The fully-utilized quota for Parastichopus represents an 11.4% annual harvest rate on the current harvestable biomass estimate, and signs that this rate is unsustainable include: low density in shallow waters, a relative abundance that has remained depressed, and a continuous decline in catch-per-unit-effort (CPUE). Abundant Parastichopus below harvestable depths may not be of sufficient density to act as a consistent reservoir to replenish the shallows with recruits. The partially-utilized quota for Mesocentrotus represents a 3.9% annual harvest rate on the current biomass estimate, relative abundance has increased from a recent low, and there is no trend in CPUE. Numerous similarities between the two fisheries with regard to fleet composition and harvest history, coupled with diverging stock status, suggest that the sea cucumber fishery may be slower to recover from over-exploitation. Despite the challenges of co-managing the fisheries among several stakeholder groups, agreement has been reached to improve the long term viability of the Parastichopus fishery using reduced harvest quotas and a closure during peak spawning months, and to continue to closely monitor the Mesocentrotus fishery.

Explaining Patterns of Pelagic Fish Abundance in the Sacramento-San Joaquin Delta

Investigating the effects of environmental, biological, and anthropogenic covariates on fish populations can aid interpretation of abundance and distribution patterns, contribute to understanding ecosystem functioning, and assist with management. Studies have documented declines in survey catch per unit effort (CPUE) of several fishes in the Sacramento-San Joaquin Delta, a highly altered estuary on the US west coast. This paper extends previous research by applying statistical models to 45 years (1967–2012) of trawl survey data to quantify the effects of covariates measured at different temporal scales on the CPUE of four species (delta smelt, Hypomesus transpacificus; longfin smelt, Spirinchus thaleichthys; age-0 striped bass, Morone saxatilis; and threadfin shad, Dorosoma petenense). Model comparisons showed that along with year, the covariates month, region, and Secchi depth measured synoptically with sampling were all statistically important, particularly in explaining patterns in zero observations. Secchi depth and predicted CPUE were inversely related for all species indicating that water clarity mediates CPUE. Model comparisons when the year covariate was replaced with annualized biotic and abiotic covariates indicated total suspended solids (TSS) best explained CPUE trends for all species, which extends the importance of water clarity on CPUE to an annual timescale. Comparatively, there was no empirical support for any other annualized covariates, which included metrics of prey abundance, other water quality parameters, and water flow. Top-down and bottom-up forcing remain important issues for understanding delta ecosystem functioning; however, the results of this study raise new questions about the effects of changing survey catchability in explaining patterns in pelagic fish CPUE.

Proof of concept for a novel procedure to standardize multispecies catch and effort data

The effect of variability in targeting needs to be removed from catch-per-unit-effort (CPUE) data to estimate reliable abundance indices for multispecies fisheries. We test a Generalized Additive Model (GAM) that includes principal component scores (PCs) derived from the species composition in the catch, called the ‘Direct Principal Component’ (DPC) procedure, for its ability to remove the effect of variable targeting. Biomass trends are simulated for two multispecies, multi-habitat fishery scenarios: (i) four species distributed differentially across two habitats and (ii) ten species distributed differentially across four habitats. Tweedie distributed CPUE records are generated from the biomass trends for a fishery with constant targeting (control scenarios) and time-varying targeting (test scenarios). The DPC procedure is simulation-tested for its ability to estimate the underlying biomass trends for all species relative to the non-standardized CPUE index. The DPC procedure proved to be more accurate compared to nominal CPUE trends in the test scenarios. Even in the control scenarios, the DPC procedure offers greater accuracy for the estimated year effect by removing substantial variation from the data, with a small penalty on the accuracy of the underlying abundance trend. However, caution is advised if the DPC-derived index diverges noticeably from alternative models despite no indications for shifts in targeting. A selection procedure based on eigenvalues of the PCs is suitable to identifying the best-performing number of PCs to include in the GAM. The DPC procedure should be applicable for a variety of multispecies fisheries.

Kuujjua River Arctic Char: Monitoring Stock Trends Using Catches from an Under-Ice Subsistence Fishery, Victoria Island, Northwest Territories, Canada, 1991 – 2009

A standardized, harvest-based monitoring program was conducted during the main under-ice subsistence fishery for Arctic char (Salvelinus alpinus) of the Kuujjua River for 18 winter fishing seasons between 1991 and 2009. The program was a response to the concern of Ulukhaktok residents that Arctic char were becoming fewer in number and smaller in size. Mean harvests averaged 1225 (SD 262) Arctic char annually for 1996–2002 and 568 (SD 274) in 2003–09, or roughly 40% and 20% of the harvest levels estimated for 1971–78 (2900, SD 842) and 1988–92 (2943, SD 1072). There was no statistical relationship between the size of the annual harvest (number of fish), and the corresponding mean annual catch per unit effort (CPUE) value (R2 = 0.0141, p = 0.761). Arctic char were fully recruited to the fishery at age nine, with 82.4% of the sampled catch (n = 3288) ranging between 8 and 12 years and composed almost exclusively (99%) of non-spawning adults. Over the time series, temporal trends were not detected (p &gt; 0.05) in mean annual CPUE (27.3 Arctic char/100 m/24 h, SD 14.15), mean fork length (593 mm, SD 78.1), or mean age (9.9 years, SD 2.0). Annual mortality rate showed a weak, but significant, decreasing trend over the series (R2 = 0.354), and there were no statistical trends in annual values of the Brody growth coefficient (R2 = 0.1337, p = 0.164). Variation in mean annual somatic condition indices was correlated with timing of sea ice clearance in spring (R2 = 0.474, p = 0.002), probably because prey quality, quantity, or both are higher in summers following earlier spring blooms in the marine environment. Together, the absence of temporal trends in CPUE, fork length, and age of the harvested fish and the apparent improvement in survival (lower mortality), suggest that the stock has been stable at the harvest levels observed during the monitoring period. The stock may also be realizing some improved fitness, which is due to changes in environmental productivity and appears to be linked, at least in part, to the timing of spring breakup in eastern Amundsen Gulf.

Comparing Fisher Interviews, Logbooks, and Catch Landings Estimates of Extraction Rates in a Small-Scale Fishery

Researchers are turning to alternative data sources (e.g., resource user knowledge) to provide information required for wildlife management. Little is known about the reliability of data elicited from resource users relative to data obtained from user-independent approaches (e.g., observations of fish catches). We test for consensus among three methods that quantify past (1996 to 2007) seahorse catch-per-unit-effort (CPUE) for a small-scale, data-poor fishery in the Philippines: interviews with fishers about good, bad, and typical catch; fisher logbooks; and observations of catch landings. Interviews and logbooks indicated no trends in CPUE through time, consistent with results from the fisher-independent metric, catch landings. Although interview estimates of “typical” CPUE greatly exceeded “typical” observed catches and logbook estimates, interview estimates of “bad” CPUE were comparable. Catch landings estimates for a fisher in a particular year were uncorrelated to what he reported during retrospective interviews. Interviews should be used cautiously to inform specific catch targets (e.g., total allowable catches), although including interview questions about a range of catch experiences (e.g., good, bad and typical), may improve interview-derived data. Logbooks are particularly useful for capturing information about fishing expeditions that produce no fish, which are largely missed by other methods.

Standardizing catch and effort data of the Taiwanese distant-water longline fishery in the western and central Pacific Ocean for bigeye tuna, Thunnus obesus

Abstract Catch per unit effort (CPUE) is often used as an index of relative abundance in fisheries stock assessments. However, the trends in nominal CPUE can be influenced by many factors in addition to stock abundance, including the choice of fishing location and target species, and environmental conditions. Consequently, catch and effort data are usually ‘standardized’ to remove the impact of such factors. Standardized CPUE for bigeye tuna, Thunnus obesus, caught by the Taiwanese distant-water longline fishery in the western and central Pacific Ocean (WCPO) for 1964–2004 were derived using three alternative approaches (GLM, GAM and the delta approach), and sensitivity was explored to whether catch-rates of yellowfin tuna and albacore tuna are included in the analyses. Year, latitude, and the catch-rate of yellowfin explained the most of the deviance (32–49%, depending on model configuration) and were identified consistently among methods, while trends in standardized catch-rate differed spatially. However, the trends in standardized catch-rates by area were found to be relatively insensitive to the approach used for standardization, including whether the catch-rates of yellowfin and albacore were included in the analyses.

An initial assessment of sampling procedures for juvenile pallid sturgeon in the Missouri River downstream of Fort Randall Dam, South Dakota and Nebraska

Summary We compared the effectiveness of passive gill nets, hoop nets, set lines, and drifted trammel nets, towed beam trawls and otter trawls to develop criteria to best determine the mean catch per unit effort (CPUE) for juvenile pallid sturgeon (Scaphirhynchus albus) based on selectivity and seasonal efficiency in various habitats of the Missouri River downstream of Fort Randall Dam, South Dakota. Sampling occurred from April to November in 2003 and 2004 and from March to November in 2005. We captured 29 juvenile pallid sturgeon in a total of 498 overnight gill net sets, 55 in 870 drifted trammel nets, 19 on 1683 set lines, and six in 166 otter trawl tows. No pallid sturgeon were captured in 515 beam trawl tows or 520 overnight hoop net sets. Seasonal trends in mean CPUE were found and the relative precision was the greatest in October and November for gill nets, in August for trammel nets, in April for set lines, and in October for otter trawls. A higher proportion of pallid sturgeon captures for gill nets were in the inside bend macrohabitat generally associated with lower water velocities, trammel nets over sand substrate and in the outside bend macrohabitat typically associated with higher water velocities and greater depths, set lines in lower water velocities, and otter trawls in depths >2.5 m and over sand substrate. Although we found trends among seasons and habitats for gill nets, trammel nets, set lines, and otter trawls, the catch rates were low and annual point estimates of relative abundance are not adequate to detect changes in relative abundance of juvenile pallid sturgeon in this reach of the Missouri River. Independently, gill nets, trammel nets, and otter trawls likely captured the size structure of the population of pallid sturgeon in the Missouri River downstream of Fort Randall Dam. Based on our results, a standardized protocol can now be established to systematically monitor juvenile pallid sturgeon, an essential element for determining responses to recovery efforts in the Missouri River.

Trends in Abundance and Mean Size of Fish Captured in Gill Nets from Minnesota Lakes, 1983–1997

AbstractWe investigated seasonal and 15‐year trends in catch per unit effort (CPUE) and mean weight of black crappies Pomoxis nigromaculatus, ciscoes Coregonus artedi, northern pike Esox lucius, walleyes Sander vitreus (formerly Stizostedion vitreum), white suckers Catostomus commersoni, and yellow perch Perca flavescens captured in gill nets from 433 Minnesota lakes between 1983 and 1997. Seasonal trends were modeled using least‐squares linear and polynomial regressions, and interannual trends were investigated with a linear mixed‐effects model and an augmented serially alternating design. Four of the six species exhibited significant seasonal trends. Walleye CPUE increased linearly, whereas walleye and cisco mean weight and northern pike CPUE decreased linearly from spring through fall. Cisco CPUE and yellow perch mean weight exhibited curvilinear relationships, decreasing from spring through summer and then increasing from summer through fall. Two species exhibited significant 15‐year trends across Minnesota from 1983 to 1997: Walleyes experienced significant positive trends in both CPUE and mean weight, probably benefiting from more efficient stocking or warmer June temperatures, and black crappies experienced a significant decreasing trend in CPUE, possibly due to replacement by walleyes, loss of spawning habitat, or increased harvest by recreational anglers. Catches of ciscoes, northern pike, white suckers, and yellow perch in gill nets were unchanged across Minnesota between 1983 and 1997, indicating population stability. The results of this study suggest that lakes should be sampled with gill nets at the same time of year or that catches should be corrected to a common date to allow direct comparisons among lakes. The monitoring of trends in fish populations and habitat variables using standardized sampling on broad spatial scales should be more widely used to detect changes, generate hypotheses regarding these changes, and focus research and management efforts.

Tests of the robustness of habitat-standardized abundance indices using simulated blue marlin catch - effort data

This paper describes a computer model designed to simulate longline catch–effort data, and to test the robustness of methods to standardize the relative catch per unit effort (CPUE) abundance index. The model considers abundance and catch by month, area and depth based on the temperature habitat of the species. Characteristics of fishing gears are used in a submodel to predict catch rate by set and depth. An application to an Atlantic blue marlin bycatch fishery from 1956 to 1999 is presented. The depth distributions of sets, the propensity of marlin to bite stationary moving baits, and the assumed habitat preferences were each varied. The simulated CPUE series were standardized using both habitat-based and General Linear Models (GLM). Unstandardized CPUE trends were strongly biased. The GLM standardizations accurately reflected trends in the simulated population. The habitat standardizations proved accurate when the assumptions used in the analysis were precisely correct, but were often strongly biased when the assumptions were inaccurate. These results suggest that habitat standardization of CPUE time series is potentially useful if there is accurate knowledge of the distributions of the population, the actual fishing depths of the gears and factors that may affect the fish's propensity to take bait. Absent certain knowledge of these factors, the habitat approach to standardization should be used with great caution.