Fishery-independent Surveys Research Articles

A long-term view on recent changes in abundance of common skate complex in the North Sea

Following decades of declines, populations of large fish recently started to increase in the North Sea, presumably due to reduced fishing pressure. However, population recovery may be too readily claimed, since standardised sampling of fish stocks commenced only in the 1970s, well after many species had already collapsed. A true recovery must be seen from a long-term perspective. The critically endangered common skate (Dipturus batis, Rajidae) species complex is an example of a large-bodied fish that mostly disappeared before standardised monitoring took place. Here, we put the recent increase in population size into a 120-year perspective, throughout three geographical divisions in the North Sea. We analysed a large range of mostly undisclosed historical data and contemporary sources. A reconstruction of Dutch commercial landings data confirms that the species used to be very abundant between 1901 and 1920, and shows how it steadily declined from 1920 onwards until it got extirpated around 1970. Based on a quantitative analysis of standardised catch numbers from fishery-independent surveys time, we conclude that the current abundance of the species is still below historical baselines and represents a local recovery at most. We further demonstrate a prominent and consistent pattern in size distribution, with larger (mature) individuals only occurring in the northern North Sea. A large dataset on historical stomach contents from the central North Sea confirmed the diet of young common skate, which consisted predominantly of shrimps. Our review exemplifies the importance of marine historical ecology to deduce the natural richness of the North Sea.

Use of management strategy evaluation to understand the value of citizen science in managing an iconic California recreational fishery

Data-limited fisheries present significant challenges to fisheries management around the world. Landings data represent the simplest and most common source of fishery information, but length data of harvested species can offer particularly useful insight into the strength of fishing pressure and the status of stocks. However, unbiased length data can be difficult and costly to collect, which highlights a need for understanding the utility of non-conventional data collection programs, such as those generated by community members and citizen science programs to improve management decision-making. In this study, our objective was to understand the value of citizen science for management using the iconic California recreational red abalone (Haliotis rufescens) dive fishery. To accomplish this, we employed management strategy evaluation (MSE) to simulate this benthic invertebrate fishery that was sampled by two different fishery independent survey protocols: a community science survey program led by trained volunteers and a professional science survey program led by a state agency. We subjected the data to a range of uncertainties, by including time-varying life history parameters, environmental variability, and effective sample size scenarios, to understand the management level consequences of each survey methodology. Our results show that community science program data collection can serve as a high-quality data source, can be linked directly to fisheries management decisions via a Harvest Control Rule (HCR), and can be a useful information source even in the absence of conventional data sources. Our results are specific to the California red abalone fishery, but they also highlight the potential broader value of community science data collection programs for improving information content of small-scale and recreational fisheries.

Long-term changes in the spatio-temporal distribution of snailfish Liparis tanakae in the Yellow Sea under fishing and environmental changes

Tanaka’s snailfish (Liparis tanakae) is a low-economic but ecologically important fish in the Yellow Sea, which is one of the most threatened marine ecosystems in the world due to environmental changes and human activities. Although it serves as both a dominant species and an apex predator, our knowledge about the long-term changes in the spatio-temporal distribution of this snailfish remains limited in the threatened ecosystem. In this study, by developing eight alternative vector autoregressive spatio-temporal (VAST) models including various combinations of sea surface temperature (SST), fishing pressure (FP) and the density of the prey (DP), we investigated the spatio-temporal distribution patterns of snailfish based on fishery-independent surveys conducted between 2003 and 2019 and examined the relative importance of different covariates. We found that SST was the most important factor in explaining variation in encounter probability and DP was the most important factor in explaining temporal variation in biomass density of snailfish. Surprisingly, incorporation of FP in the spatio-temporal models neither improved explanation of the variance in encounter probability nor biomass density. Based on Akaike’s information criterion, we selected a spatio-temporal model with SST in preference to seven alternative models. The inter-annual distribution range of snailfish was relatively stable whereas the spatial patterns varied over time. In 2003–2006 and 2011, the hotspots of snailfish were widely distributed throughout almost the entire Yellow Sea area. In contrast, in other survey years, especially in 2007–2009, 2015–2016 and 2019, the distribution was more concentrated within the central Yellow Sea. No significant shift in centers of gravity (COGs) was detected for the population. The estimated effective area occupied correlated significantly with biomass density of snailfish (r = -0.71, P< 0.05). Outputs from this study enhanced our understanding of how and the extent to which multiple pressures influence the observed long-term changes in spatio-temporal distribution of snailfish in the Yellow Sea.

Integrating trawl and longline surveys across British Columbia improves groundfish distribution predictions

Predictions of the distribution of groundfish species are needed to support ongoing marine spatial planning initiatives in Canadian Pacific waters. Data to inform species distribution models are available from several fishery-independent surveys. However, no single survey covers the entire region and different gear types are required to survey the range of relevant habitat. Here, we demonstrated a method for integrating presence–absence data across surveys and gear types that allows us to predict the coastwide distributions of 65 groundfish species in British Columbia. Our model leverages data from multiple surveys to estimate how species respond to environmental gradients while accounting for differences in survey catchability. We find that this method has two main benefits: (1) it increases the accuracy of predictions in data-limited surveys and regions while having negligible impacts on accuracy when data are already sufficient, and (2) it reduces uncertainty, resulting in tighter confidence intervals on predicted occurrences. These benefits are particularly relevant in areas of our coast where our understanding of habitat suitability is limited due to a lack of spatially comprehensive long-term groundfish surveys.

From policy to practice: Addressing bycatch for marine species-at-risk in Canada

Unintended bycatch of depleted or vulnerable marine species is an unsolved conservation issue that undermines the sustainability of fisheries worldwide. In Canada, policy incentives to address bycatch of vulnerable species-at-risk have become more prominent in recent years. Yet bycatch risk has been difficult to quantify and mitigate, in part due to large data gaps in fisheries observation and monitoring. Here we suggest the use of novel modelling frameworks to optimize spatial management strategies for bycatch mitigation. We utilize spatiotemporal modeling of fisheries-independent survey data to predict high-risk regions for three at-risk skates (family Rajidae) in Atlantic Canada. We use these identified regions to evaluate the relative reduction in bycatch risk that can be expected by closing targeted bycatch-protection zones on the western Scotian Shelf to bottom-trawl fishing, and further examine the relative costs to the fishing industry that such closures may impose. We show that when closures are precisely targeted on high-bycatch risk areas, relative costs to industry are minimal by affected fishing area (1.25 ± 0.62 % total area) or displaced landings (0.28 ± 0.14 % by weight of catch). To reduce bycatch risk by 50 % for all three vulnerable skates, less than 10 % of landed catch weight is displaced. These results can be used to reduce bycatch encounters for any endangered, threatened or protected species through spatially targeted conservation measures. We conclude that new approaches to the analysis and mitigation of spatial-temporal bycatch patterns can help to meet regulatory or market-driven requirements for bycatch reduction at low cost.

Two scales of distribution and biomass of Antarctic krill (Euphausia superba) in the eastern sector of the CCAMLR Division 58.4.2 (55°E to 80°E).

Regular monitoring is an important component of the successful management of pelagic animals of interest to commercial fisheries. Here we provide a biomass estimate for Antarctic krill (Euphausia superba) in the eastern sector of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) Division 58.4.2 (55°E to 80°E; area = 775,732 km2) using data collected during an acoustic-trawl survey carried out in February and March 2021. Using acoustic data collected in day-time and trawl data, areal biomass density was estimated as 8.3 gm-2 giving a total areal krill biomass of 6.48 million tonnes, with a 28.9% coefficient of variation (CV). The inaccessibility of the East Antarctic makes fisheries-independent surveys of Antarctic krill expensive and time consuming, so we also assessed the efficacy of extrapolating smaller surveys to a wider area. During the large-scale survey a smaller scale survey (centre coordinates -66.28°S 63.35°E, area = 4,902 km2) was conducted. We examine how representative krill densities from the small-scale (Mawson box) survey were over a latitudinal range by comparing krill densities from the large-scale survey split into latitudinal bands. We found the small scale survey provided a good representation of the statistical distribution of krill densities within its latitudinal band (KS-test, D = 0.048, p-value = 0.98), as well as mean density (t-test p-value = 0.44), but not outside of the band. We recommend further in situ testing of this approach.

Bycatch in the California halibut (Paralichthys californicus) Trawl Fishery

Bycatch rates within the California halibut trawl fishery were calculated using landed catch data from 1997–2020 fishery logbooks and estimated using landed and discarded catches from 2002–2019 fishery observer data. Average bycatch rates were significantly different between the two datasets. The average bycatch ratio estimated from fishery logbooks was 0.36 ± 0.17 while the average bycatch ratio estimated from the observer data was 4.61 ± 1.29, based on the weight of bycatch to weight of California halibut catch. Additionally, the most frequently caught bycatch species were estimated for each dataset. Bycatch rates calculated from the observer data were closely aligned with fishery-independent surveys conducted by the California Department of Fish and Wildlife, signaling the importance of using fishery observers to obtain estimates of bycatch within the California halibut fishery. Spatial patterns of bycatch revealed that fishing effort was highest near Monterey, San Luis Obispo and Ventura. Our results suggest that data from logbooks alone are not sufficient to adequately estimate bycatch within the California halibut trawl fishery.

Sea‐surface temperature anomalies mediate changes in fish richness and abundance in Atlantic and Gulf of Mexico estuaries

AbstractAimAnthropogenic warming of marine systems has caused biological and physiological responses that are fundamentally altering ecosystem structure. Because estuaries exist at the land‐ocean interface, they are particularly vulnerable to the effects of ocean warming as they can undergo rapid biogeochemical and hydrological shifts due to climate and land‐use change. We explored how multiple components of estuarine fish diversity—turnover, richness, and abundance—have changed in the North Atlantic and Gulf of Mexico estuaries across space and time and the drivers of change.LocationNorth Atlantic and Gulf of Mexico.TaxaFish.MethodWe compiled long‐term (>30 years), continent‐wide fisheries independent trawl surveys conducted in estuaries—from the Gulf of Maine to the Gulf of Mexico (U.S. waters)—and combined these with climate and land‐use‐land‐cover data to examine trends and ecological drivers of fish richness, abundance and turnover using mixed‐effect models.ResultsSpecies richness, abundance and turnover have increased in North Atlantic and Gulf of Mexico estuaries in the last 30 years. These changes were mediated largely by sea‐surface temperature anomalies, especially in more northern estuaries where warming has been relatively pronounced.Main ConclusionThe increasing trajectory of turnover in many estuaries suggests that fish communities have changed fundamentally from the baselines. A fundamental change in community composition can lead to an irreversible trophic imbalance or alternative stable states among other outcomes. Thus, predicting how shifting community structures might influence food webs, ecosystem stability, and human resource use remain a pertinent task.

Detection and quantification of differences in catch rates among research vessel gears and commercial vessels

Commercial fishing vessels can be a cost-effective alternative to research vessels for performing towed gear fishery-independent surveys, if catch rates are comparable among commercial vessels and with research vessels. A parallel fishing experiment was conducted off the coast of Wales, United Kingdom, to compare the king scallop (Pecten maximus) catch rates of three commercial vessels using commercial dredges and a research vessel using two types of scientifically modified dredges. The scientific dredges are currently used in the fishery-independent survey of local scallop populations. Size-structured scallop catch-per-unit-effort (CPUE) was compared among vessel-gear combinations. Two similarly sized commercial vessels had generally similar CPUEs, however there were some significant differences with scallop size. A smaller commercial vessel had significantly lower CPUEs for a broad range of scallop sizes. The research vessel dredges had significantly higher CPUE for smaller scallops than the commercial vessels. Vessel size is likely to be driving the differences among commercial vessels and belly ring size is likely to be driving differences among research and commercial dredges. These findings highlight commercial vessel CPUE should not be assumed the same, whilst also showing that vessel size may be the best indicator of catch rate similarity. These results also highlight that changing the fishery-independent vessel and gear to the commercial options trialled here would result in a considerable loss of information about the smaller scallops in the population. These findings will be of interest to fishery scientists or managers using multiple vessels, or considering a change of vessels, for fishery-independent surveys.

Variation in growth, length and age characteristics of estuarine Acanthopagrus (Sparidae) populations in New South Wales, Australia

Knowledge of spatial variation in growth and demographic characteristics of exploited teleost populations is informative for understanding levels of resilience and susceptibility to environmental and anthropogenic perturbations and for resource management. This study investigated variation in length- and age-compositions, length-at-age and growth, longevity and mortality of Acanthopagrus (A. australis, A. butcheri and their hybrids) population complexes across seven estuaries spanning seven degrees of latitude in eastern Australia. Populations were sampled using two gears according to standardised fishery-independent survey protocols. Populations within each estuary displayed considerable variation in length-at-age, with sex-specific growth attributes evident in some estuaries but not others. Nevertheless, females dominated populations, and on average, the mean lengths and ages of females were greater than males within each estuary population. Estuary type and location appeared to influence the estuary-specific growth characteristics of both sexes, with populations in the southern coastal lakes having, on average, greater mean lengths at age and faster growth than those in the northern riverine estuaries. Length and age compositions of populations did not vary accordingly, with observed longevities and estimated natural mortalities varying among estuaries, most likely reflecting estuary-specific environmental conditions and anthropogenic activities. In general, populations across all estuaries primarily comprised fish <25 cm fork length (FL) and 10 years of age. Given their potential to reach FLs up to 50 cm and ages >20 years, populations across most estuaries appeared length and age truncated. Ecological relationships and resource management implications are discussed.

Thirty-five years of tiger shark Galeocerdo cuvier relative abundance near Bimini, The Bahamas, and the Southeastern United States with a comparison across jurisdictional bounds.

Abundances of large sharks are reported to have declined worldwide, and in response various levels of fisheries management and conservation efforts have been established. For example, marine-protected areas have been suggested as a means to protect large expanses of ocean from fishing and other industrial activities (e.g., habitat destruction), and in 2011 The Commonwealth of The Bahamas established The Bahamas Shark Sanctuary. Nonetheless, assessing the effectiveness of conservation efforts is challenging because consistent long-term data sets of shark abundances are often lacking, especially throughout the Caribbean and The Bahamas. In this study, the authors investigated the catch rates and demographics of tiger sharks Galeocerdo cuvier caught in a fishery-independent survey near Bimini, The Bahamas, from 1984 to 2019 to assess relative abundance trends following the banning of longline fishing in 1993 and the subsequent establishment of the shark sanctuary. To contextualize the relative abundance trends near Bimini, the authors compared this to the relative abundance of tiger sharks in a fishery-dependent survey from the Southeastern USA (SE USA), conducted from 1994 to 2019. The data of this study suggest that local abundance of tiger sharks has been stable near Bimini since the 1980s, including after the ban of longline fishing and the implementation of the shark sanctuary. In comparison, the abundance near the SE USA has slowly increased in the past decade, following potential declines in the decade preceding the USA Shark Management Plan. The results of this study provide some optimism that current conservation efforts in The Bahamas have been effective to maintain local tiger shark abundance within the protected area. In addition, current fisheries management in the SE USA is allowing this species to recover within those waters.

Change in cephalopod species composition in the overexploited coastal China seas with a closer look on Haizhou Bay, Yellow Sea

Climate change and intensive fishing have affected not only population abundance, but also species composition. Cephalopods have been increasing in abundance in the world ocean under climate change due to their flexible life-history traits, including the over-exploited China Seas. Despite the increasing importance of coastal cephalopods in the China Seas, there have been no reports of changes in either species composition, nor the ecological roles of species with different life-history traits. Thus, this study first presents the changes in species composition of coastal cephalopods throughout the China Seas as summarized from fishery-independent survey reports over the last six decades. This is followed by an investigation of species composition of cephalopods in Haizhou Bay in the Yellow Sea. The ecological roles of two currently targeted cephalopods, Amphioctopus fangsiao and Loliolus spp. (Loliolus beka and Loliolus japonicus), are evaluated using an ecosystem model. The species composition of coastal cephalopods in the China Seas has changed since the 1960s, from species of large size and high value to small-size, low-value species. Cephalopod species composition in Haizhou Bay shows great seasonality, which is probably due largely to the characteristics of their life cycle. The population abundance of A. fangsiao and Loliolus spp. appear to be affected by ambient water temperature, and population distribution of Loliolus spp. seems to correlate with water depth. Occupying the highest trophic level in this ecosystem, A. fangsiao potentially displays strong top-down control over other organisms. Loliolus spp. are keystone species showing higher keystoneness in the autumn, owing to a low abundance of fish species which normally prey on them. The species-specific life-history traits and ecological roles of cephalopods are therefore important factors to consider in order to manage them effectively.

Evidence for spatiotemporal shift in demersal fishery management priority areas in the western Mediterranean

Marine protected areas (MPAs) are a promising management tool for the conservation and recovery of marine ecosystems, as well as fishery management. MPAs are generally established as permanent closures but marine systems are dynamic, which has generated debate in favour of more dynamic designs. As a consequence, the identification of priority areas should assess their persistence in space and time. Here, we develop a step-by-step approach to assess the spatiotemporal dynamics of fishery management priority areas using standard fishery-independent survey data. To do so, we fit Bayesian hierarchical spatiotemporal SDM (species distribution model) models to different commercially important demersal species and use the resulting maps to fit different spatial prioritisation configurations. The proposed method is illustrated through a western Mediterranean case study using fishery-independent trawl survey data on six commercially important species collected over 17 years. We use these results to assess the spatiotemporal dynamics of fishery priority areas. We identified two fishery priority area patterns in the study area, each predominant during a different time period of the study, asserting the importance of regularly reassessing MPA designs.

Long-term decline in northern pike (Esox lucius L.) populations in the Baltic Sea revealed by recreational angling data

In the Baltic Sea, the large predatory fish northern pike (Esox lucius L.) is important for both recreational fisheries and ecosystem functioning. As existing fishery-independent surveys do not adequately monitor pike populations, a general lack of knowledge on population status and trends poses challenges for management. Here we use recreational angling data as an alternative method to describe pike population development along the Swedish Baltic Sea coast from 1938 onwards and assess the change over time in potential mortality factors by estimating harvest by fisheries and consumption by large predators. Data from a Swedish national register on trophy-sized pike (>12 kg) showed that numbers and maximum sizes peaked in 1990–1995, after which declines in both metrics are evident. In logbooks from a sport fishing club in the Stockholm archipelago, a simultaneous decrease in maximum sizes of pike was observed, together with a decrease in the total number of pike caught per fishing day. Jointly, these data indicate a decline in the abundance of large pike since around 1990. While commercial pike fisheries in the Baltic Sea have decreased continuously since the 1950s, recreational fishing increased after 1985, when Swedish coastal waters were made open access to anglers. The declines in large pike starting in the 1990s could, thus, have been driven by an increase in mortality from recreational fisheries, which at the time primarily practiced catch and kill. Since the 2000s, bag and slot length limits, spawning closures, and a general increase in catch-and-release fishing has reduced the landings of pike in recreational fisheries. Despite these fisheries regulations and higher release rates the decline in catches of large pike has continued, indicating an effect of other mortality factors. The strong growth of grey seal (Halichoerus grypus) and great cormorant (Phalacrocorax carbo sinensis) populations suggest that predation pressure on pike has increased over time. In the Stockholm archipelago these two predators were estimated to remove 5–18 times (range based on different diet composition estimates) more pike biomass than total fisheries landings in 2014–2017. To improve the situation for northern pike in the Baltic Sea managers need to consider both fisheries restrictions and measures to decrease predation pressure and increase recruitment. Catch data from recreational fisheries may be used to evaluate such management efforts by providing information on the population development of this keystone species.

Understanding transboundary stocks’ availability by combining multiple fisheries-independent surveys and oceanographic conditions in spatiotemporal models

Abstract Shifts in the distribution of groundfish species as oceans warm can complicate management efforts if species distributions expand beyond the extent of existing scientific surveys, changing the proportion of groundfish available to any one survey each year. We developed the first-ever model-based biomass estimates for three Bering Sea groundfishes (walleye pollock (Gadus chalcogrammus), Pacific cod (Gadus macrocephalus), and Alaska plaice (Pleuronectes quadrituberculatus)) by combining fishery-independent bottom trawl data from the U.S. and Russia in a spatiotemporal framework using Vector Autoregressive Spatio-Temporal (VAST) models. We estimated a fishing-power correction to calibrate disparate data sets and the effect of an annual oceanographic index to explain variation in groundfish spatiotemporal density. Groundfish densities shifted northward relative to historical densities, and high-density areas spanned the international border, particularly in years warmer than the long-term average. In the final year of comprehensive survey data (2017), 49%, 65%, 47% of biomass was in the western and northern Bering Sea for pollock, cod, and plaice, respectively, suggesting that availability of groundfish to the more regular eastern Bering Sea survey is declining. We conclude that international partnerships to combine past data and coordinate future data collection are necessary to track fish as they shift beyond historical survey areas.

Development of an industry-funded fishery-independent survey and associated indices for managing a deep sea crab resource in Western Australia

The inclusion of fishery-independent data in stock assessments has been shown to have positive stock and financial outcomes for fisheries. A co-management approach between the government and commercial fishers in this limited-entry fishery led to the successful implementation of industry-funded, fishery-independent surveys of crystal crab, a deep water Geryonid crab, in two areas off Western Australia.While the instigation of these surveys was driven by a need for improved abundance indices for stock assessment, they have also provided an opportunity to better understand stock dynamics and composition. Structuring the surveys across the depth distribution (400–700 m) of crystal crabs demonstrated an apparent lack of depth-related size stratification in crystal crabs with large crabs captured throughout the species depth distribution. Female crabs, which mature below the legal minimum size for harvest, were a minor component of the catch and were more prevalent at the shallower end of their depth distribution. There also appeared to be a movement of pre-molt crabs to the periphery of their distribution (shallow and deep), in preparation to molt.There was a slight decline in the fishery-independent abundance (FIA) index from 2017 to 2019 mirroring the pattern displayed by the current standardized commercial catch rate, with an increase during the most recent survey (2020). The FIA index will be incorporated as an additional data source for the weight of evidence and size-structured integrated model for the assessment of the crystal crab resource off the west coast of Western Australia.The surveys, which were funded by industry and supported by government research staff onboard, have proved cost-effective, robust and sustainable, and a preferable means by which fishery-independent data could be collected for this commercially important Geryonid crab. The cost of the survey was partially offset by the retention of the legal catch. Such a collaborative model could be applied in fisheries world-wide to address the inherent biases of commercially-derived indices and the ever-increasing financial constraints on regulators to conduct stock assessments.

Performance evaluation of fixed-station sampling design for a fishery-independent survey with multiple objectives

Performance evaluation of fixed-station sampling design for a fishery-independent survey with multiple objectives

A tale of two species: Vermilion and sunset rockfish in the Southern California Bight

The vermilion rockfish complex consists of two distinct species, vermilion rockfish (Sebastes miniatus) and sunset rockfish (S. crocotulus) with clear haplotypic differences. Due to a one-way mitochondrial introgression from vermilion into sunset rockfish a high proportion (20–30%) of fish with a vermilion haplotype are characterized as sunset based on nuclear genotype (introgressed sunset, hereafter, introgressed). Here we examined differences in the distribution and biological attributes of vermilion and sunset rockfish (including introgressed individuals) collected during a fisheries independent groundfish survey conducted with hook and line gear in the Southern California Bight in 2014. We saw significant differences in spatial distribution (latitude, depth, and distance from the nearest port and mainland) and biological characteristics (average size, size frequency distribution, weight-length and size-depth relationships) between vermilion rockfish and both introgressed and sunset rockfish but no differences between sunset and introgressed fish. Our analyses established that introgressed and sunset rockfishes shared similar biological and geographic characteristics, with no significant differences based on the features we examined. Consequently, we explored the relationship between the catch of vermilion rockfish collected per site, relative to the combined presence of vermilion, introgressed and sunset rockfishes, and a suite of co-located environmental and geographic variables using binomial generalized additive models (GAMS). The best model explained 95.0% of the deviance, indicating that the occurrence of vermilion, introgressed, and sunset rockfishes depended on latitude, longitude, depth, dissolved oxygen, temperature and distance from port.

Assessing the size selectivity of capture gears for reef fishes using paired stereo-baited remote underwater video

All methods used to sample fish populations exhibit some degree of size selectivity, whether due to the physical properties of the gear, behavioral responses to the gear, or the spatial distribution of the targeted population. In most stock assessments, selectivity functions are assumed and their parameters estimated due to a paucity of empirical data necessary to estimate selectivity. However, incorrect assumptions about selectivity functions can impart significant bias, ultimately affecting assessment outcomes. In 2016, a study was conducted to assess the size selectivity of three fishery-independent survey methods for reef fish in the U.S. South Atlantic: (1) a chevron trap survey, (2) a standardized repetitive timed drop hooked-gear survey, and (3) an unstandardized hooked-gear survey designed to mimic industry fishing practices. Each survey method was paired with a stereo-baited remote underwater video (S-BRUV) camera, which was treated as a comparative reference, considering that it is the least selective of the four gears used. A total of 93 stations were sampled with all gear types, and size data were analyzed for three managed reef fishes: red snapper, Lutjanus campechanus (all gears), black sea bass, Centropristis striata (all gears), and vermilion snapper, Rhomboplites aurorubens (all gears except chevron traps). For red snapper, all three capture gears showed dome-shaped selectivity, the degree of doming being more pronounced for chevron traps as evidenced by a decreasing capture probability for individuals over ~500 mm FL. Despite the largest red snapper (> 800 mm FL) being observed more often on S-BRUV, mean size of red snapper was generally smaller on S-BRUV than for either hooked-gear survey, indicating that hooked-gears capture proportionally fewer smaller red snapper. For black sea bass, there was evidence of flat-topped selectivity for all gear types, but chevron traps captured smaller individuals on average than did hooked gears. For vermilion snapper, both hooked gears exhibited dome-shaped selectivity. Given these results it’s clear that improper assessment of selectivity can lead to poor assumptions about the sampled population. Therefore, when the selectivity function of a particular gear type is not explicitly known, studies that directly estimate selectivity should be conducted to reduce assumptions applied to assessments. This study demonstrates the utility of non-destructive video surveys to complement and evaluate the selectivity functions of standard fisheries assessment methods. Furthermore, efforts to broaden the spatial scale of this study’s survey methods, expand the species to be examined, validate collected life history data, and determine the potential influence of interannual recruitment variability on observed selectivity patterns are necessary to better understand selectivity processes for all reef fishes assessed in the region.

Comparison of catch in multifilament and monofilament gill nets in a long-term survey on Lake Michigan

Long-term fishery independent surveys provide metrics of relative abundance and contribute biological information critical to effective fisheries management. Improvements in technology and manufacturing processes have had profound effects on gear efficiency. In Lake Michigan, a standardized multi-agency fish community survey was adopted in 1998 which used multifilament nets to survey nearshore fish communities. Contemporary commercial gill netting operations largely utilize monofilament nets because they’re less expensive, more durable and thought to be less visible and therefore more efficient. As such, interest in converting long-term agency surveys to monofilament nets has grown. To compare catch rates and the size of fish collected, we set similarly configured nets of both mesh materials on the same day at standard survey locations. The most common species captured in the survey were lake trout (52%), yellow perch (19%), lake whitefish (15%), longnose sucker (8%), white sucker (4%) and burbot (1%). Monofilament nets were more efficient in capturing lake whitefish and longnose sucker and equally efficient in capturing other species. On average, nearly three times (2.85) as many lake whitefish were captured in monofilaments nets, and two times as many longnose suckers (2.13). Larger lake whitefish and yellow perch were captured in monofilament nets, whereas lake trout were slightly smaller. For other fish species, similar sizes were captured in each net material. This evaluation incorporated broad replication (298 paired nets) and representation from diverse locations and depth strata in Lake Michigan to inform gear conversion efforts and allow for adjustments as needed in gear conversion efforts.