Gear Saturation Research Articles

Taking the bait: Environmental factors affecting bait retention and hook disposition in the Gulf of Maine Bottom Longline Survey

Longline fishery surveys are major contributors to groundfish species abundance estimates. Catchability is often assumed constant, but bait is lost or consumed at inconsistent rates during and across gear sets. Accounting for hook availability and gear saturation can improve abundance estimates, but these data are challenging to collect. Our objectives were to determine whether video camera systems can be used to collect these data from the Northeast Fisheries Science Center’s Gulf of Maine Bottom Longline Survey and to explore the associations between hook disposition percentages and environmental characteristics. Electronic monitoring camera systems were deployed on partner vessels during two fall and two spring seasons to capture video of gear retrieval. During post-survey review, individual hooks were recorded as one of the following hook dispositions: bait, empty hook, fish, and invertebrate. Percentages of these hook dispositions were characterized across categorical (season, day or night, and bottom substrata) and continuous (bottom temperature, bottom depth, and substrate rugosity) survey station variables. Nonmetric multidimensional scaling and logistic regression analyses revealed correlations between retained bait and low bottom temperatures, the spring season, shallow depths, rough bottom substrata, and high terrain rugosity. These characteristics were typical of shallow, inshore, and topographically variable survey strata, suggesting that catchability differs among habitat types. This information will be incorporated into catch rate models to develop standardized indices of abundance for groundfish stock assessments. This study is an example of the utility of electronic technologies to supplement on board data collection during cooperative fishery surveys.

A spatial analysis of longline survey data for improved indices of Atlantic halibut abundance

Abstract Atlantic halibut (Hippoglossus hippoglossus) support an economically important fishery on the eastern coast of Canada. Like other species that are not well sampled by trawl surveys, halibut in this area are monitored using longline surveys. These surveys present challenges that can make obtaining indices of abundance difficult. Issues include gear saturation, which can result in a non-linear relationship between catch per unit effort and local abundance. The current approach to obtain a relative index consists of fitting a multinomial exponential model to a subset of hooks from each survey station. While this approach accounts for hook competition, it does not account for the presence of spatial patterns. We therefore extend the multinomial exponential model to include spatial random fields for both Atlantic halibut and non-target species, set-specific soak time, and data from the hooks. Furthermore, we propose a method for aggregating the resulting spatially varying indices to obtain an annual index for the entirety of the modelled area. This novel approach identifies Atlantic halibut hotspots in multiple years, while simultaneously providing relative abundance indices for 2017 through 2020. These outcomes demonstrate the widespread applicability of our methods for improving the scientific advice upon which fisheries management decisions are based.

Azorean demersal longline survey abundance estimates: Procedures and variability

Survey data from the Azores is used for fisheries stock assessments under the ICES Working Group on the Biology and Assessment of Deep-sea Fisheries Resources (WGDEEP) covering deep open ocean areas. The Azores research cruise using bottom longlines for abundance estimation is probably unique in the Northeast Atlantic Ocean. This study analyzed data from annual Azorean bottom longline surveys (ICES subdivision 10a2) from 1996 to 2018 to calculate abundance indices of commercial demersal species, to estimate the statistical significance of the annual changes in the abundance estimates, and to examine the possible factors that cause this variability. The catch rates of these surveys appear to provide accurate indices of abundance for most of the commercially important demersal species. The observed inter-annual variability of the survey abundance estimates can be explained by survey effort distribution, fishery dynamics, aggregation patterns of some species, habitat preferences, fish movements, and environmental effects. However, other factors can affect these estimates (soak time, gear saturation and competition for hooks) and we recommend that additional studies be undertaken to understand these effects.

Time versus Space: Choice of Effort Metric Can Avoid Bias in Boat Electrofishing Catch per Unit Effort

AbstractWhile catch per unit effort (CPUE) is the most widely used metric for expressing and comparing boat electrofishing catch data, “effort” has been inconsistently defined. Boat electrofishing guidelines refer to both time‐ and distance‐based metrics, with little consensus about the appropriateness of one over the other. Catch rate metrics that use time‐based effort may potentially be biased by gear saturation due to handling time. We evaluated the potential for bias resulting from effort metric choice by comparing catch rates based on one temporal and two spatial effort metrics—time, shoreline length, and a GPS‐based areal measurement—using 3 years of data from 288 sampling occasions when all three metrics were recorded simultaneously. We used pairwise comparisons to isolate the effect of effort metric choice and fit six candidate models to each potential pair of CPUE metrics: a simple linear model, four models with separate slopes for survey variables (lake, season, night or day, and habitat), and an asymptotic model. The best‐fit model was asymptotic when the time‐based CPUE metric was compared with both space‐based metrics, and the linear model accounting for habitat was the best‐fit model for the comparison between both spatial methods. These results indicate that using a time‐based measure of effort resulted in hyperstable CPUE when fish densities were high due to gear saturation. By comparison, spatial measures of effort were robust to changes in fish density. Observed habitat‐based variation in the relationship between the two spatial metrics suggests that a CPUE measurement based on shoreline distance is adequate for assessing trends in abundance within waters or areas with homogenous habitat but not locations with contrasting conditions. We recommend the use of an areal‐based effort metric due to its robustness to gear saturation, comparability between waters, and potential for incorporating other variables that influence the performance of CPUE.

Investigating three sources of bias in hook-and-line surveys: survey design, gear saturation, and multispecies interactions

Hook-and-line surveys can be used to estimate population trends in fish species where conventional methods such as trawl, acoustic, visual, or pot surveys cannot be applied. Hook-and-line surveys allow for the collection of biological information, but the resultant indices of abundance may be biased. We designed simulations to address concerns around survey design, hook saturation, and competition among species and found that catch per unit effort (CPUE) declined more slowly than population size across all scenarios. This hyperstability was most prominent when fish were found in high-density patches, and these scenarios have median absolute relative error values roughly three to five times greater than those with more even distributions of fish density. Despite hyperstability, the surveys still had statistical power to detect changes in abundance. Interspecific competition for hooks caused bias in survey results when one species was more aggressive than another. Taken together, our results indicate hook-and-line surveys fill a niche in survey methodologies, but their use and interpretation can be challenged by hyperstability and competition among species.

Evaluating catchability in a large-scale gillnet survey using hydroacoustics: Making the case for coupled surveys

Abundance estimates facilitate successful fisheries management. Fisheries agencies often monitor abundance through fishery independent standardized protocols generating relative measures such as catch-per-unit-effort (CPUE), where CPUE is assumed proportional to true abundance. Unfortunately, this assumption is rarely met as fish behavior and environmental conditions influence catchability and sample gear efficiency. We used paired gillnet and hydroacoustic samples and a catchability equation (Ui = qNiβ) to assess the correspondence between gillnet CPUE (Ui) and hydroacoustic abundance estimates (Ni). We found that gill nets were hyperstable (i.e., β < 1) and efficiency declined along environmental gradients. These gradients, such as increased depths, and decreased turbidity and water temperatures, likely influenced fish behavior, and encounter and gear saturation rates. As a result, catchability declined with increasing abundance qacross survey regions. Finally, simulations showed that catchability gradients and variable migratory patterns can contribute to annual variation in CPUE indices regardless of changes in abundance. Surveys plagued by varying catchability could benefit from coupling with hydroacoustics, a sample gear less subject to gear efficiency and catchability issues.

Habitat-specific performance of vertical line gear in the western Gulf of Mexico: A comparison between artificial and natural habitats using a paired video approach

Gear performance is often assumed to be constant over various conditions encountered during sampling; however, this assumption is rarely verified and has the potential to introduce bias. We used fishery-independent vertical line surveys to evaluate whether gear efficiency and selectivity is similar while assessing reef fish populations at oil and gas platforms, artificial reefs, and natural banks in the western Gulf of Mexico. We conducted 192 vertical line sets with cameras placed on a subset of these deployments to validate any differences in efficiency among habitat types. Red snapper (Lutjanus campechanus) accounted for 93% of the catch. No difference in red snapper CPUE among habitats was detected. When evaluating fish size, 8/0 and 11/0 hooks sampled significantly larger red snapper at natural banks than at artificial habitats. While CPUE was similar among all hooks at artificial habitats, CPUE at natural banks was lower for shallower hooks and increased towards the bottom hooks along the backbone. At all habitats, red snapper TL decreased from shallow to deep hook positions. Simultaneous camera deployments revealed other processes affecting efficiency such as bait removal and depredation. Vermilion snapper (Rhomboplites aurorubens) were effective at removing bait while avoiding capture. Perhaps related to this observation, Red snapper CPUE was negatively correlated with the vermilion snapper video index of abundance. Video confirmed gear saturation was prevalent (70% of deployments), occurring more frequently on artificial habitats. Furthermore, the time fished was effectively “shorter” at artificial habitats as the number of available baited hooks declined rapidly. These results point towards higher relative abundance at artificial habitats; however, the prevalence of saturation indicates vertical line CPUE may not always be proportional to true abundance, hindering our ability to detect differences at the scale examined in this study. Vertical line surveys should evaluate the prevalence of saturation as inferences regarding relative abundance may be compromised when this information is unknown.

Baited Remote Underwater Video surveys undercount sharks at high densities: insights from full-spherical camera technologies

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 585:113-121 (2017) - DOI: https://doi.org/10.3354/meps12395 Baited Remote Underwater Video surveys undercount sharks at high densities: insights from full-spherical camera technologies James P. Kilfoil1,*, Aaron J. Wirsing2, Matthew D. Campbell3, Jeremy J. Kiszka1, Kirk R. Gastrich1, Michael R. Heithaus1, Yuying Zhang1, Mark E. Bond1 1Department of Biological Sciences, Florida International University, North Miami, FL 33181, USA 2School of Environmental and Forest Sciences, University of Washington, Seattle, WA 98195, USA 3National Marine Fisheries Service, Southeast Fisheries Science Center, Mississippi Laboratories, Pascagoula, MS 39567, USA *Corresponding author: jkilf001@fiu.edu ABSTRACT: Video surveys are an essential tool for monitoring marine communities. Their use to study elasmobranch populations has dramatically increased over the last decade. However, the restricted field-of-view (FOV) of traditional cameras in these surveys may bias abundance estimates in a number of ways, including saturation at high densities and low detection probability for rare or cryptic species. This study investigated these potential biases using newly developed full-spherical (FS) camera technology. A comparison of 35 Baited Remote Underwater Video surveys (BRUVs), using both FS and traditional cameras, was conducted from July to August 2016 in shallow waters (0.4 to 8.5 m) of Tetiaroa, French Polynesia. Both blacktip reef Carcharhinus melanopterus and sicklefin lemon sharks Negaprion acutidens were quantified from traditional cameras using MaxN and MeanCount methods. These estimates were then regressed against FS cameras counts, which were assumed to more accurately represent site abundance, to test for gear saturation. Detection probabilities of the traditional and FS cameras were assessed using a Bayesian binomial model, with uninformed-uniform priors. Results indicated a significant effect of gear saturation for standard BRUVs as counts on FS cameras increased, regardless of the metric used. Furthermore, traditional cameras had a significantly lower detection probability (mean ± 2 SD: 69.88 ± 0.008%) than FS cameras (81.20 ± 0.007%). Our findings show that traditional cameras are unlikely to adequately discriminate differences in shark relative abundance at high densities. Therefore, standard BRUV techniques that use restricted FOV cameras are likely limited in their ability to provide accurate information to managers once populations have reached particular thresholds of abundance. KEY WORDS: 360° cameras · Detectability · Elasmobranchs · Monitoring · Video surveys Full text in pdf format Supplementary material PreviousNextCite this article as: Kilfoil JP, Wirsing AJ, Campbell MD, Kiszka JJ and others (2017) Baited Remote Underwater Video surveys undercount sharks at high densities: insights from full-spherical camera technologies. Mar Ecol Prog Ser 585:113-121. https://doi.org/10.3354/meps12395 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 585. Online publication date: December 22, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Using Electrofishing Catch Rates to Estimate the Density of Largemouth Bass

AbstractCatch rates are commonly used to indirectly index population density, e.g., nighttime electrofishing to survey Largemouth Bass Micropterus salmoides populations. However, the relationship between catch rate and population density must be known in order for catch rate to serve as an accurate index. We sought to determine if Largemouth Bass electrofishing catch rate was linearly or nonlinearly correlated to population density in high density populations using measurement‐error models and Monte Carlo simulations. Previous studies of the relationship between Largemouth Bass electrofishing catch rate and density have occurred in low‐density populations (&lt;50/ha). We hypothesized that high‐density Largemouth Bass populations may result in gear saturation during electrofishing sampling, i.e., too many fish for dipnetters to capture resulting in missed captures. This would therefore underrepresent the population's density. The nighttime electrofishing catch rate of 66–294 Largemouth Bass/h was linearly related to their population density (77–152/ha) over 15 experimental events. The linear relationship suggests electrofishing catch rate is an appropriate index of population density in similar high‐density Largemouth Bass populations.Received August 11, 2014; accepted December 3, 2014

Fish and fisher behaviour influence the vulnerability of groupers (Epinephelidae) to fishing at a multispecies spawning aggregation site

Targeted fishing of spawning aggregations is a major contributor to extinction risk in numerous species of grouper (Epinephelidae). Marine reserves are often used to protect spawning aggregation sites, including multispecies sites shared by several species of grouper. However, marine reserves may be biologically, socioeconomically or culturally unviable in some fisheries, and alternative management actions must be explored. Implementing effective management actions that control rather than prohibit fishing requires an improved understanding of how species vary in their vulnerability to fishing gears and respond to changes in fishing effort. To estimate sources of variability in vulnerability to fishing (i.e. catchability), catch-per-unit-effort (CPUE) and other fisheries data were collected in parallel with underwater visual census-derived estimates of aggregation size at a multispecies spawning site of Epinephelus fuscoguttatus and E. polyphekadion. Despite having similar abundances, E. polyphekadion was eightfold more vulnerable to capture by hook-and-line gear, clearly outcompeting its congener for bait. Contrasting with the common assumption of a proportional relationship, the CPUE of both species was unrelated to the size of their respective aggregations. Moreover, the CPUE of each species was unrelated to hook size and depth fished. However, E. polyphekadion CPUE declined as the density of fishing effort increased at the site, with gear saturation identified as the likely mechanism for this effect. E. fuscoguttatus CPUE was negatively related to the size of aggregations formed by its congener, stemming from the superior competitiveness and therefore higher selectivity of the gear for E. polyphekadion. Our findings demonstrate that CPUE is an unreliable indicator of spawning aggregation status. The other sources of variation in CPUE that we identify have implications for gear-based management, which must be based on understanding of gear selectivity for aggregating species, and fishing effort controls, which must consider the potential for effort-dependent patterns in catchability.

Maximization of revenue in fishery model with Cobb-Douglas type of production function

The paper considers the effects of congestion and gear saturation in the harvesting of fishery model given by logistic type of differential equation. It applies continuous dynamic control programming technique (Bellman in Dynamic programming, Princeton University Press, Princeton, 1957; Bertsekas, Dynamic programming—deterministic and stochastic model, Princeton Hall, Englewood Cliffs, 1987) to maximize the net revenue obtained by nonlinear production function of Cobb-Douglas type.

High lacustrine gillnet catchability of anadromous Arctic charr

Arctic charr is the only freshwater fish in most of the High Arctic, with both resident, anadromous, and landlocked populations present. The anadromous Arctic charr is particularly highly sought-after, and has been an important food source for people living in Arctic regions. A recent decline in harvest in many areas has been related to over-exploitation by extensive gillnetting. Very few studies, if any, have estimated the gillnet efficiency for harvesting anadromous Arctic charr. In this study, all anadromous Arctic charr ascending the lake, Linnevatn, in western Spitsbergen, Svalbard, were marked over a period of 5 weeks, in July–August 2008. Recaptures in the lake were obtained by gillnetting with three mesh sizes (39, 45, and 52 mm measured knot-to-knot) during three periods. The total number of anadromous charr in the lake was estimated by both Schnabel and Petersen mark-recapture methods. The catchability increased significantly with fish size. Anadromous charr in the length-class 40.0–56.9 cm captured by the legal mesh size in Svalbard lakes (52 mm) had a mean catchability of 0.0023 per gillnet per 2 h fishing effort, and the catch quota which is set at 40 charr for Linnevatn by the Governor of Svalbard, would have been filled by less than five gillnets, each used for 6 h. Although this short fishing time may give an overestimation of catchability due to the avoidance of gear saturation, the high catchability values still indicate that anadromous Arctic charr populations may be extremely vulnerable to gillnetting. Hence, in addition to catch quotas set for each population, a restriction on the number of gillnets allowed per harvester should also be considered.

Qualitative observations of Dungeness crabs, Cancer magister, in and around traps: evidence of resource guarding and clustering

Decapod crustaceans are well known for agonistic interactions where they commonly fight over resources. Accurate descriptions of crab behaviour are essential to the development of quantitative behavioural studies involving the Dungeness crab fishery. An underwater video system mounted over a commercial crab trap in situ was used to qualitatively describe several of the most common behaviours utilized by Cancer magister in and around traps, including the documentation of previously undescribed behaviours in this species. Crabs commonly guarded trap doors without entering the trap and prevented other inspecting crabs from entering the trap. Agonistic interactions in traps ceased when crabs ‘clustered’ together, creating a group of non-interacting, fairly motionless crabs sitting on or near each other. These observations indicate that crab behaviour merits further attention in future studies of gear saturation and the catchability of Dungeness crabs.

Electrofishing Catchability of Walleyes, Largemouth Bass, Smallmouth Bass, Northern Pike, and Muskellunge in Wisconsin Lakes

AbstractWe sought to determine whether electrofishing catchability was density dependent and varied with physical and biological factors for walleyes Sander vitreus, largemouth bass Micropterus salmoides, smallmouth bass M. dolomieu, northern pike Esox lucius, and muskellunge E. masquinongy in Wisconsin lakes. Electrofishing catch rate (number of fish caught per shoreline mile) was linearly related to population density (number of fish per acre) in spring for largemouth bass, northern pike, and muskellunge and in fall for walleyes, largemouth bass, and smallmouth bass. In contrast, gear saturation caused the electrofishing catch rate to be nonlinearly related (hyperstable) to population density for walleyes and smallmouth bass during spring. Catchability was higher during spring than fall for walleyes, largemouth bass, and smallmouth bass. Catchability of walleyes during fall was positively related to the percentage of littoral zone, whereas catchability of largemouth bass, smallmouth bass, and muskellunge was negatively related to the shoreline development index. Other physical and chemical variables failed to describe significant residual variation in catchability of any other species in any other season. We conclude that population density cannot be accurately estimated from the electrofishing catch rates of walleyes and smallmouth bass during spring. Therefore, mark–recapture methods must still be used to estimate population density if managers choose to sample those species during spring in Wisconsin lakes.

An experimental assessment of the impact of gear saturation on an abundance index for an exploited rock lobster resource

Increased fishing effort may downwardly bias indices of abundance, such as catch-per-unit-effort (CPUE), due to gear saturation. A field experiment was developed to assess gear-saturation effects on an index of relative abundance used for stock-assessments of rock lobster, Palinurus gilchristi, off South Africa. A progressive decrease in the value of the index, which is derived from commercial trap catch rates after accounting for the influences of vessel characteristics, trap soak-times, depth, area and month, has led to cuts in the total allowable catch (TAC) over the past 10 years. Concerns have been raised, however, that recent steep increases in fishing effort might have led to gear saturation effects, so that the index may now underestimate abundance relative to periods of lower effort, and hence the resource may not have declined to the extent that the index suggests. In the experiment, the fishing grounds were subdivided into the Agulhas Bank and Eastern fishing grounds, and both areas were subjected to three 2-month treatments of either unrestricted fishing effort or reduced fishing effort. In both areas, fishing in the first 2 months was unrestricted. In the second 2-month period, the number of trap-days was reduced by 25–30%, whereas in the third 2-month period this number was further reduced on the Agulhas Bank (by 65%), but increased by 25% on the Eastern fishing grounds. In terms of the saturation hypothesis, CPUE was predicted to rise during periods when effort was reduced. Changes in CPUE were assessed by expressing CPUE during periods of reduced effort as a proportion of CPUE during periods of unrestricted effort. These proportions were compared to proportions for equivalent time periods in previous years (1991–1998) when fishing effort was always unrestricted. The null hypothesis that CPUE is unaffected by effort (i.e. no gear-saturation effect) was rejected in only one of four treatments. In the other three treatments, the experiment failed to separate responses to effort-manipulations from those due to seasonal and areal fluctuations in catchability. However, a model that integrates the results of all four treatments suggests that, if GLM-standardized effort is used as the index of potential saturation, there is only a 2.5% probability that saturation could account for as much as 0.004 of the drop in CPUE from 0.15 to 0.09 kg tails/trap between 1991/1992 and 1997/1998. If trap-days instead are used as the saturation index, this 0.004 figure increases, but only to 0.03. This thus suggests with very high probability that saturation effects cannot alone explain the drop in CPUE in the fishery during the 1990s.

Catch estimation in the presence of declining catch rate due to gear saturation.

One strategy for estimating total catch is to employ two separate surveys that independently estimate total fishing effort and catch rate with the estimator for total catch formed by their product. Survey designs for estimating catch rate often involve interviewing the fishermen during their fishing episodes. Such roving designs result in incomplete episode data and characteristically have employed a model in which the catch rate is assumed to be constant over time. This article extends the problem to that of estimating total catch in the presence of a declining catch rate due, e.g., to gear saturation. Using a gill net fishery as an example, a mean-of-ratios type of estimator for the catch rate together with its variance estimator are developed. Their performance is examined using simulations, with special attention given to effects of restrictions on the roving survey window. Finally, data from a Fraser River gill net fishery are used to illustrate the use of the proposed estimator and to compare results with those from an estimator based on a constant catch rate.

Modelling capture processes in individual traps: entry, escapement and soak time

Stationary fishing gear is employed in a diverse array of fisheries including those for many high unit-value species. The mode of operation of these gear types (traps, long-lines, gillnets, etc.) requires special consideration in the development of abundance indices because of gear saturation effects. Specifically, factors affecting the probability of capture and of escapement or other sources of loss must be addressed. Here, we describe two models of capture processes in traps that include existing models as special cases. Deterministic models are first developed to illustrate the basic principles. Stochastic analogues of two well-known models are then described using the theory of birth–death stochastic processes. It is shown that the mean of the stochastic models is identical to the deterministic case for models where closed form solutions are possible. The stochastic models provide additional diagnostic information in terms of the variance and the probability distribution of catch levels. Illustrations of this approach are provided for experimental observations on ingress and catch for the American lobster (Homarus americanus).

A stock survey technique using the time to capture individual fish on longlines

Longline catches per unit of effort (CPUE) from research surveys are often assumed to vary in proportion to fish abundance. This assumption, however, may be invalid if the abundance of the target species is high enough to saturate the gear or if the abundance of nontarget species is high enough to exclude the target species from capture. We examine a new approach to surveying fish populations with longlines that is based on time-to-capture data measured with small, fish-activated timing devices attached to every hook. A new measure of relative abundance, λ, is developed that is immune to the effects of gear saturation and interspecific competition for hooks. Two estimators of λ are compared by using capture-time data collected during summer 1987–1991 for pelagic armorhead (Pseudopentaceros wheeleri). Both estimators are shown to be unbiased if the underlying assumptions are true and fairly robust to the observed departures from these assumptions.

Effectiveness of Crab and Lobster Traps

Traps are a versatile and powerful fishing gear. Desired species and sizes can be targeted through trap design and the choice of bait. Size of the catch is affected by trap size, bait quantity and quality, time between setting and hauling, and preventing escape through the entrance. But the largest potential for increasing trap catches is by increasing ease of entry and reducing the effect of gear saturation (animals inside traps preventing those outside from entering). Using catch per trap as an index of abundance is attractive for both fisheries management and ecological studies. However, correlations between catch and abundance have not been well established, probably because of the many factors affecting catchability (e.g. stage of the molt and reproductive cycles, sex, animal size, lunar and diurnal cycles, temperature, and water motion). Methods for conducting trapping surveys, measuring catchability, and comparing fishing strategies are critically reviewed.