Variability In Catch Per Unit Effort Research Articles

The paralarval stage as key to predicting squid catch: Hints from a process-based model

Squid species show pronounced interannual variability in population size. While this may partially reflect changes in fisheries pressure, it is thought to be primarily the result of environmental variability. Most squid have an annual life cycle with only a short period dedicated to reproduction. With little overlap between generations, the environment can exert a major influence on stock size. In this study we explore, through a combination of process-based modelling and statistical analysis, whether environmental variability explains variability in catch of the chokka squid, Loligo reynaudii, over the Agulhas Bank off South Africa. We focus on growth and survival during the first two months spent as “paralarva” in the pelagic. This period has been suggested to be a key bottleneck and a potential predictor of catch. To describe prey availability and predation pressure, we develop a dynamic model of the size spectrum (1 mg–1000 kg) of the ecosystem over the Agulhas Bank, with trophic interactions governed by size. In tandem, we develop a model for the growth of individual L. reynaudii, which specifies where in the size spectrum individual squid can be found at each stage of their development. We find a correlation of 0.74 between modelled biomass representative for L. reynaudii at the end of its paralarval stage and catch per unit effort (CPUE) in the subsequent season in the period 1995–2015. This suggests that the paralarval stage is indeed a bottleneck: modelled food availability and predation pressure experienced by paralarvae explains 55% of the variability in CPUE, which is a proxy for spawning stock biomass. As the paralarval stage ends approximately nine months before the time of spawning and maximum catch, this work could be used to develop catch predictor with a nine-month lag.

Japanese and Taiwanese pelagic longline fleet dynamics and the impacts of climate change in the southern Indian Ocean

Climate change is projected to continue shifting the distribution of marine species, leading to changes in local assemblages and different interactions with human activities. With regard to fisheries, understanding the relationship between fishing fleets, target species catch per unit effort (CPUE), and the environment enhances our ability to anticipate fisher response and is an essential step towards proactive management. Here, we explore the potential impact of climate change in the southern Indian Ocean by modelling Japanese and Taiwanese pelagic longline fleet dynamics. We quantify the mean and variability of target species CPUE and the relative value and cost of fishing in different areas. Using linear mixed models, we identify fleet-specific effort allocation strategies most related to observed effort and predict the future distribution of effort and tuna catch under climate change for 2063–2068. The Japanese fleet's strategy targets high-value species and minimizes the variability in CPUE of the primary target species. Conversely, the Taiwanese strategy indicated flexible targeting of a broad range of species, fishing in areas of high and low variability in catch, and minimizing costs. The projected future mean and variability in CPUE across species suggest a slight increase in CPUE in currently high CPUE areas for most species. The corresponding effort projections suggest a slight increase in Japanese effort in the western and eastern study area, and Taiwanese effort increasing east of Madagascar. This approach provides a useful method for managers to explore the impacts of different fishing and fleet management strategies for the future.

A fishery-independent survey of juvenile shortfin mako (Isurus oxyrinchus) and blue (Prionace glauca) sharks in the Southern California Bight, 1994–2013

A fishery-independent abundance survey was initiated by the National Marine Fisheries Service (NMFS) and the California Department of Fish and Game (CDFG) in 1994 to track the relative abundance and size of juvenile shortfin mako (Isurus oxyrinchus) and blue (Prionace glauca) sharks in the Southern California Bight (SCB). The survey was designed based on data from an experimental commercial shark longline fishery that operated in the SCB during 1988–1991. Survey sets were conducted annually during the summer months within seven 10×10min spatial blocks in the SCB close to the California Channel Islands. Between 1994 and 2013, survey effort totaled 460 sets. The standardized catch-per-unit-effort (CPUE) of shortfin mako showed a generally declining trend from 1994 through 2010 with increases during the final years to a level similar to those of the mid-1990s. For blue sharks, the standardized CPUE showed a generally declining trend throughout the time series with the lowest values in 2012 and 2013, and an anomalously high CPUE in 2000. Catch rates varied across the survey area with fewer, larger sharks caught in the more northern blocks of the survey. Sharks of age classes 0–2 represented the majority of those caught in the survey (approximately 81% of blue sharks and 58% of makos), yet there was variability in the sizes of blue and mako sharks caught by year. The sex ratio of age-0 sharks caught was not different from 1:1 for shortfin makos, but skewed toward females for blue sharks. Although the survey area is relatively small and results show interannual and spatial variability in CPUE that is not fully understood, these data represent the first and only fishery-independent survey that has targeted these shark species in the SCB. The results of the survey and associated data provide useful information regarding regional relative abundance, size- and sex-compositions, and spatial distributions of shortfin mako and blue sharks, all of which are essential for stock assessments and fisheries management.

Within‐lake distribution patterns of fish assemblages: the relative roles of spatial, temporal and random environmental factors in assessing fish assemblages using gillnets in a large and shallow temperate lake

In this study, the relative role of spatio-temporal factors and associated environmental variables (water transparency and temperature) were quantified in relation to gillnet samples of fishes in a large and shallow lake (Lake Balaton, Hungary). Most of the variance (56·1%) in the relative abundance data (%) was related to the vertical segregation of fishes. This gradient substantially affected the catch per unit effort (CPUE) by number of the dominant species, the surface-oriented bleak Alburnus alburnus and the benthic common bream Abramis brama. It also influenced total CPUE, mean fish mass and species richness and diversity. At the lake level, horizontal habitat heterogeneity (i.e. littoral v. offshore) accounted for only 8·3% of the total variance in relative abundance data, but was important in structuring the CPUE of the ruffe Gymnocephalus cernua and the pikeperch Sander lucioperca. The longitudinal environmental gradient (i.e. lake basin), year and season of sampling, water transparency and temperature had significant effects on relative abundance only at the habitat level, but were also important components of variability of CPUE in some species at the lake level. As sampling schemes need to consider the main gradients in fish assemblage distributions, the use of surface and pelagic gillnets should be more intensively incorporated in the study and monitoring of fish assemblages in shallow lakes and lake habitats.

Catch per unit effort standardization of the eastern Bering Sea walleye pollock (Theragra chalcogramma) fleet

Abstract A general linear model (GLM) was used to standardize catch per unit effort (CPUE) data for Alaska walleye pollock (Theragra chalcogramma) from the Bering Sea fleet for the years 1995–1999. Data were stratified temporally by year and season and spatially by area using either Alaska Department of Fish and Game (ADFG and that this relationship differed between dedicated catcher vessels and offshore catcher processors. Coefficient estimates and response surfaces generally indicated increased CPUEs with the percentage of pollock in the haul and showed mixed results with vessel speed. The vessel identification number incorporated most vessel characteristics, leaving vessel speed primarily as a fitting variable with less biological meaning. The year/area/season stratification procedure was found to be necessary due to the unbalanced design, which otherwise would have factor levels with no data in a large combined model. In addition, the stratification procedure reduced the variability in CPUE substantially.

Abundance of Ohio Shrimp (Macrobrachium ohione) and Glass Shrimp (Palaemonetes kadiakensis) in the Unimpounded Upper Mississippi River

Large rivers of the United States have been altered by construction and maintenance of navigation channels, which has resulted in habitat loss and degradation. Using 7 y of Long Term Resource Monitoring Program data collected from the unimpounded upper Mississippi River, we investigated Ohio and Glass Shrimp abundance collected from four physical habitats of the unimpounded upper Mississippi River: main channel border, main channel border with wing dike, open side channel and closed side channel. Our objective was to assess associations between Ohio and Glass Shrimp abundance, environmental measurements and the four habitats to better understand the ecology of these species in a channelized river system. Ohio Shrimp were most abundant in the open side channels, while Glass Shrimp were most abundant in the main channel border wing dike habitat. Thirty-two percent of the variance in Glass Shrimp abundance was explained by year 1995, year 1998, water temperature, depth of gear deployment, Secchi disk transparency and river elevation. Approximately 8% of variation in Ohio Shrimp abundance was explained by Secchi disk transparency. Catch-per-unit-effort (CPUE) was greatest in 1998 for Glass Shrimp but lowest in 1997. Conversely, CPUE was greatest in 1996 for Ohio Shrimp and lowest in 2000. Both species exhibited inter-annual variability in CPUE. Long-term impacts of river modifications on aquatic invertebrates have not been well documented in many large river systems and warrants further study. The findings from this study provide ecological information on Glass and Ohio Shrimp in a channelized river system.

Analysis of the factors affecting crustacean trawl fishery catch rates in the northern Tyrrhenian Sea (western Mediterranean)

The aim of this study was to analyse the main factors affecting catch rates of the most important decapod crustaceans of the bottom trawl fishery in the northern Tyrrhenian Sea, western Mediterranean. Catch per unit effort (CPUE) data (kg/fishing day/boat) of deep water rose shrimp, Parapenaeus longirostris, Norway lobster, Nephrops norvegicus, and red shrimps, Aristaemorpha foliacea and Aristeus antennatus, were collected monthly in the years 1991–1999 at the auction of Porto Santo Stefano, where these species are traditionally exploited by trawlers using traditional trawl nets. The application of cluster analysis to the entire data set allowed the identification of three main “metiers” or fishing tactics, corresponding to different fishing grounds, species assemblages and characteristics of vessels. Two “metiers” corresponded to fishing activity targeting the above-mentioned crustacean species. Generalised linear modelling was used to investigate the influence of factors such as month, year and vessel on catch rates of the species studied. This model explained a considerable amount of variability in the CPUE data, which substantially reflected the differences observed in the trends of monthly landings of these species. Month was an important factor explaining deviance in the CPUE for the deep water rose shrimp, but especially for the two red shrimps. This was mostly due to the temporal pattern in the catchability of these species, as well as the seasonality of the fishing effort targeting these resources. Year significantly contributed to the variation in CPUE of all the species studied, in particular for P. longirostris, confirming that the abundance of this species is subject to distinctive inter-annual fluctuations. Vessel was a significant factor determining variability in CPUE for P. longirostris and, especially, in N. norvegicus. No single boat characteristic such as length, gross registered tonnage and engine power provided a more satisfactory explanation than the vessel factor as a whole. For Norway lobster, the high variation explained by the vessel is attributable to the fact that the fishing fleet targeting this species was the most heterogeneous, involving two different “métiers” and, therefore, boats differing in size and in fishing practices.

Variance and cost-benefit analyses to determine optimal duration of tows and levels of replication for sampling relative abundances of species using demersal trawling

The effects on catch per unit effort (CPUE) of trawlable species due to the duration of tows and temporal and spatial heterogeneity were examined using demersal trawling in the prawn grounds off the east coast of New South Wales, Australia. Standard trawls in a triple-rig configuration were used in a nested experimental design to compare catch rates in tows of various durations, during the day and night, in shallow and deep fishing grounds. Significant effects from all these factors were detected, but the kinds and degrees of these effects differed among variables. To determine the degree of spatial and short-term temporal variability in CPUE, a pilot survey was completed where replicate tows were done at various locations on replicate days (school prawn grounds) and nights (king prawn grounds). Cost-benefit analyses determined optimal CPUE estimates of species given (i) the time available to survey a location during any sample period, and (ii) the sizes of variances among tows and days/nights. The consequences of this replication on the sizes of standard errors in subsequent sampling were estimated. A uniform and optimal methodology was developed which is currently being used in surveys of the New South Wales prawn trawl grounds.

Exploring the association between swordfish catch rates and thermal fronts on U.S. longline grounds in the western North Atlantic

Associations between ocean surface thermal fronts and the swordfish catch rates of U.S. longline vessels were explored. The study area was the western North Atlantic off the United States, extending from 32°N to 45°N and from 76°W to 63°W. To locate and describe fronts, we used three variables computed from satellite-derived sea surface temperature (SST): horizontal gradient, distance to nearest thermal surface front, and frontal density. Most of the fishing effort analysed occurred along the edge of the continental shelf, where there was a high frequency of frontal presence. Very high catch per unit effort (CPUE) occurred more frequently in the vicinity of fronts than would be expected by chance. The high variability of CPUE that could not be explained by our frontal parameters suggested other, unmeasured, factors also influenced catch rates.

Relationships among long'term fisheries abundances, hydrographic variables, and gross pollution indicators in northeastern U.S. estuaries

ABSTRACTCategorical time series regression was applied to 55 fish stocks in the Potomac, Hudson, Narragansett, Delaware, and Connecticut estuaries for the period 1929–1975. Interannual variability in catch per unit effort (CPUE) was related to CPUE, hydrographic variables, and pollution variables, lagged back in time to represent the conditions contributing to the multiple ages comprising each fishery. Hydrographic variables included water temperature and flow in the estuary– and, for offshore spawning stocks, wind direction and magnitude–during the months of spawning and early life stage development. Pollution variables included measures of dissolved oxygen conditions in the estuaries, volume of material dredged, and sewage loading (or human population). Lagged CPUE, hydrographic variables, and pollution variables all played important roles in explaining historical variability in CPUE. Lagged CPUE was significant in 45 of 55 stocks generally accounting for 5–35% of the variability. Lagged hydrographic variables were significant in 53 of 55 stocks, explaining an additional 5–40% of the variability unaccounted for by lagged CPUE. Lagged pollution variables were significant in 35 of 55 stocks, generally accounting for an additional 5–30% of the variability not explained by lagged CPUE and hydrographic variables. Results did not exhibit expected patterns of consistency in the importance of lagged CPUE for a species across estuaries or consistency in the importance of pollution variables across estuaries. Results did exhibit the expected north‐to‐south longitudinal pattern in the importance of timing of the hydrographic variables, the months of importance being one or two months later in more northerly estuaries. Higher‐order interaction effects were important in almost all stocks that were well‐modeled by categorical time series regression. Of the 30 stocks with final regression models having R2 > 0.55, 26 stocks involved significant interaction effects, five had only significant interaction effects (no significant main effects), and 20 stocks had significant interactions involving variables not significant as main effects. The difficulties involved in analyzing long‐term trends in fish populations and partitioning variability between natural and anthropogenic sources are discussed.

Assessment of the Australian deep-water royal red prawn stock using commercial catch and effort data

Trends in standardized catch-per-unit effort (CPUE) were analyzed to assess the state of the deep-water royal red prawn ( Haliporoides sibogae) stock exploited off eastern Australia since the mid 1970s. Two aspects of uncertainty in using CPUE as an index of abundance were recognized. First, it was difficult to determine accurately the impact of the fishery on the prawn abundance because all the biological and/or technical factors influencing the CPUE could not be identified and quantified. Analyses of covariance showed that differences in vessel characteristics, period and location of fishing explained only part (33.9%) of the variability of CPUE. The second problem was related to the fact that the fishery exploited only part of the stock, and therefore, trends in CPUE reflected only trends in abundance for that part of the stock. The fishery was concentrated within 1° latitude (34°00′S–35°00′S), from 400 to 500 m deep, and declined markedly during winter months each year. These fishing patterns were more related to economic motivations than to the abundance of prawns which were apparently available year round and over a wider geographic range. Despite its limitations, analysis of CPUE provided useful information for a first appraisal of the state of the stock. The stability of annual landings (300–350 t) and standardized CPUE (300–400 kg per boat-day) since the early years of the fishery indicates that the royal red prawn stock is in a steady state under the current level of fishing effort.

Effects of soak-time and spatial heterogeneity on sampling populations of spanner crabs Ranina ranina

A series of field experiments was done in spanner crab Ranina ranina (Linnaeus) fishing grounds to determine the effects on catch per unit effort (CPUE) of crabs due to soak-time and the species' spatial heterogeneity. Standard and optimally-designed baited tangle-traps were used in a nested experimental design to catch crabs on gear set in place for various periods of time. To determine the degree of spatial and short-term temporal variability in CPUE, replicate sets of traps were set at different locations, depths and times of day. Cost-benefit analyses of this experiment yielded optimal numbers of traps and sets of traps to be used at each location and depth in subsequent sampling. The minimum time one should leave traps in the fishing grounds to achieve maximal CPUE was determined as 60 min. Different locations and depths yielded quite different CPUE's indicating that future surveys should encompass several locations and depths. Time of day had no significant effects on CPUE. Costbenefit analyses showed that 5 traps on each of 3 sets should be used at each location and depth to optimize CPUE given the limited time availabe to survey a given place. The consequences of this replication on the sizes of standard errors in future sampling were estimated. A uniform and optimal methodology is developed from the results dscussed in this and a previous paper whlch wdl be used in subsequent censussing of this species' distnbutions and abundances. Finally I discuss the worth of manipulative experimentation to test specific hypotheses about species which are sampled using baited traps and note the value of cost-benefit analyses of pilot s tud~es in designing surveys of such species' populations.