Higher Catch Rates Research Articles

Cyclical, multi-trophic-level responses to a volatile, introduced forage fish: Learning from four decades of food web observation to inform management

Abstract Species introductions can have significant effects on recipient ecosystems. Anticipating potential ecosystem change in response to introduced species based on historical information can help managers prepare for future conditions. Rainbow Smelt Osmerus mordax have been introduced widely to improve sport fish growth. As intended, Walleye Sander vitreus growth in Horsetooth Reservoir, Colorado increased after Rainbow Smelt introduction, but poor Walleye recruitment occurred as well. Additionally, opossum shrimp Mysis diluviana became absent from both predator diets and intermittent surveys, the dominant Daphnia species in Horsetooth Reservoir shifted and Daphnia densities declined significantly. These patterns were repeated during two different time periods of increased Rainbow Smelt abundance, suggesting that Rainbow Smelt have a strong influence on multiple components of the ecosystem. The repetition of responses to Rainbow Smelt offered the opportunity to evaluate indicators to anticipate potential ecosystem regime shifts that restructure predator–prey dynamics across trophic levels. Three predictors (i.e., high estimated Rainbow Smelt abundance, high catch rates of large Walleye, and low Daphnia densities) were associated with poor Walleye recruitment. Simple indicators like these could inform timely management decisions to take advantage of the benefits Rainbow Smelt offer, while lessening their undesirable effects. For example, management decisions could be made, such as preparing for Walleye egg collections, rearing and stocking of Walleye, increasing availability or quality of Walleye spawning habitat, allowing more protective or liberalized adult Walleye harvest to promote natural recruitment, and limiting Rainbow Smelt access to their spawning habitat.

Comparative study on growth performance and nutritional quality of Eriocheir sinensis between Liaohe River strain and Yangtze River strain under rice field culture environment

This study investigated the similarities and differences in catch rates, growth performance, proximate composition, amino acid content, and fatty acid profiles between the Yangtze River crab and the Liaohe River crab in rice aquaculture systems in northern China. A three-month culture experiment was conducted for the Yangtze River crab and the Liaohe River crab in a rice located at longitude 124.82° and latitude 43.50°. The results revealed that Liaohe River crab had higher catch rate and faster growth rates than Yangtze River crab, and the female crab had earlier ovaries. The edible tissues of Liaohe River crabs contain higher crude protein and fat contents, featuring a more reasonable amino acid composition and structure. Meanwhile, the gonads of male and female Yangtze River crabs had higher PUFA content. In conclusion, under the conditions of this experiment, the Liaohe River crab demonstrated a significant growth advantage.

Counteracting effects of “hook avoidance” and “hook habituation” on angler catch rates in a catch‐and‐release fishery

AbstractCatch‐and‐release (C&R) angling is often used to maintain high catch rates but fish vulnerability to capture may decrease following hooking, thereby decreasing angler catch per unit effort (CPUE) (hyperdepletion). To determine if fish post‐capture response affected recapture probability and population‐level CPUE, individual capture histories of Largemouth Bass in two lakes were compared before and after doubling angling effort in a Before‐After Control‐Impact (BACI) analysis. Previous capture and day‐of‐season both affected recapture probability. Counteracting effects of previous capture and reduced late‐season catch rates caused no hyperdepletion of angler CPUE. Our results highlight the complexity of fish behavioral responses to angling and suggest that hyperdepletion of angling catch rates may not be an issue in C&R fisheries.

Maw money, maw problems: A lucrative fish maw fishery in Papua New Guinea highlights a global conservation issue driven by Chinese cultural demand

AbstractFish maw (teleost swim bladder) is a dried seafood product valued highly by Chinese cultures in East Asia, though global supply chains are poorly understood. Here, we describe the rapid development of a fish maw fishery in a low‐income nation to illustrate how globalization can affect sustainability. In Papua New Guinea (PNG), fish maw developed into a fishery valued at ∼$831,000 USD annually between 2014–2018. Its development has been driven by Asian expatriates, who provide market access and fishing gear to local communities. The highest valued local species, scaly croaker Nibea squamosa, has a maximum value of $15,615 USD kg−1 (dried) at first‐point‐of‐sale, potentially the highest first‐point‐of‐sale fish maw product globally. Its value has led to high incidental catch rates of threatened species in an area that is a globally significant conservation stronghold. International trade databases need to recognize fish maw as a high value and globally traded product and consider a specific fish maw commodity code to assist nations in identifying emerging fish maw fisheries. Additionally, the Convention on the International Trade of Endangered Species of Flora and Fauna (CITES) could assist in protecting vulnerable fish maw species and facilitate management practices for incidentally caught threatened species.

Spatial and temporal variability of the two main caught species of an artisanal trap fishery in an oceanic island

Abstract This study analysed the catches of trap fishing in the Canary Archipelago, NE Atlantic Ocean. This study was conducted from October 2016 to September 2017, April to November 2018 and September 2020, in five ports (San Cristóbal, Taliarte, Castillo del Romeral, Arguineguín and Mogán). The primary gear were traps with small mesh size (31.6 mm) and large mesh size (50.8 mm). A total of 2587 small mesh size traps and 141 large mesh size traps were analysed from 20‐ to 130‐m depth. The main target species were Dentex gibbosus and Stephanolepis hispidus. Catches of traps with large mesh size showed D. gibbosus above first maturity and S. hispidus in small mesh size traps. Both species exhibit larger specimens during reproductive periods. The most effective traps for D. gibbosus (large mesh) were located on the western coast (>30‐m depth), with the highest catch per unit of effort (CPUE) in Mogán (857.7 g trap−1 day−1). The most effective traps for S. hispidus (small mesh) were located in southern areas, especially in sandy habitats (124.9 g trap−1 day−1 in Castillo del Romeral, 102.9 g trap−1 day−1 in Arguineguín). The highest catchability of D. gibbosus was observed in April (CPUE of 962.8 g trap−1 day−1), and the highest catchability of S. hispidus was found in June (CPUE of 165.9 g trap−1 day−1). The traps with small mesh size showed a great selectivity of sizes for S. hispidus; though high catch rates of immature specimens of D. gibbosus pose a threat to species conservation. The management recommendations' proposed measures include revising minimum catch sizes for both species. Additionally, we suggested depth limitations for mesh sizes of traps. The study highlights the need for new management strategies to ensure the conservation of targeted demersal species, with special emphasis on addressing the threat posed by small mesh sizes to immature D. gibbosus. The findings provide valuable insights for adapting fishery management practices to sustainably conserve the targeted species in the Canary Archipelago.

Shark and odontocete depredation on the catch of the tuna longline fishery in New Caledonia (South Pacific Ocean)

Abstract Large marine predators feeding on fish caught on fishing gear, referred to as ‘depredation’, occur in a wide range of fisheries worldwide. Depredation can result in negative ecological and socio-economic impacts, leading to conflict between fishers and depredating species. However, depredation remains understudied in many fisheries, and this hampers the development of effective mitigation solutions. In this study, 21 years of fishing data (2002–2022) were used to assess shark and odontocete depredation in the pelagic tuna longline fishery of New Caledonia. Using generalized linear models, the year, season, effort, soaking time, and vessel were identified as variables significantly influencing the probability of depredation to occur. Results showed that while shark depredation occurred more frequently than odontocete depredation (58.5% vs. 9.2% of the longline sets), they damaged a lower proportion of fish (3.9% vs. 12.3%) over the study period. Unlike sharks, odontocetes selectively depredate tuna, with their highest occurrence during periods of high tuna catch rates, suggesting a co-occurrence with fishing activities. Together, these results indicate that depredation in the New Caledonian fishery is high compared to other regions and provide essential information on the dynamics and impacts of the issue as a basis for considering management and mitigation options.

Investigating insect catch metrics from a large Austrian museum

Insects can damage museum collections. Heritage organisations are increasingly alert to such risk, so have moved towards integrated pest management which sees monitoring as important to conservation strategies. Museum insects are usually monitored using sticky traps, although the records these provide are not always easy to interpret or analyse, so scoring methods, pest occurrence indices and zone systems have been used to use the observations to manage pests. A six-year trapping programme at almost 700 sites (i.e. traps) across six floors of a large museum in Austria provided a total catch of ∼30 000 arthropods. Catch rate (catch per trap) was higher on lower floors although there was a substantial year-to-year variation. In addition to blunder traps, a proportion using pheromones as an attractant were effective at catching T. bisselliella. The pheromone is not attractive to silverfish (Zygentoma) yet the shy insects appear to take cover in the pheromone traps. In contrast Attagenus spp. were caught at equal rates on both pheromone and blunder traps. The study examined what factors influence the catch of insects in traps. The overall catch in a room is proportional to the number of traps set out. Catch increases with the size of the room, but this may arise because the number of traps is also related to room size. More specifically catch seems proportional to square root of room area, suggesting it relates to its perimeter. Infestations are revealed by high catch rate, maximum catches on a set of traps and the proportion of traps that are active in catching insects. The study aims to assess which parameters that might assist in identifying infested locations in museums.

Development and application of a bioenergetics growth model for multiple early life stages of an ecologically important marine fish

Spatial and temporal variability in temperature and food availability are key drivers of growth of marine fishes. Growth during the early life stages (ELS's) is tightly coupled to survival, and in turn, can set year-class strength (i.e. annual recruitment) and overall stock productivity of populations and fished stocks. Ontogenetic changes in physiology, dietary preferences, and growth across ELS's can be accounted for within bioenergetics models, but existing models lack resolution within larval and early juvenile stages. We leveraged daily output from a coupled physical-biogeochemical model to force a highly resolved ontogenetic bioenergetics model parametrized for an ecologically important rockfish in the California Current System. Size-at-age predictions closely track empirical growth trajectories of the ELS's. Scenario testing revealed that growth performance is disproportionately driven by changes in temperature compared to food availability. We then expanded the model to incorporate spatial climatological differences in temperature and prey concentration and found that preflexion growth potential is maximized in areas of historical spawning, suggesting the timing and location of reproduction is an adaptive strategy that places larvae in habitat favorable for survival. Growth potential for late-stage larvae (postflexion) is greatest over a broad areal extent, implying that if a particle tracking algorithm was coupled to the bioenergetics model, a wide range of larval dispersal pathways would place postflexion larvae in habitat suitable for rapid growth. Finally, growth potential of pelagic juveniles is maximized over the continental shelf and shelf-break, aligning with high juvenile catch rates from a fisheries-independent survey. In summary, this study (i) serves as a proof of concept that a bioenergetics model with high ontogenetic resolution can reproduce life stage-specific growth trajectories even though the underlying physiology data for model parameterization is imperfect and (ii) can aid future studies aimed at understanding how ecosystem processes interact with ontogenetic growth and changes in year class strength of early life stages of marine fishes.

Spatiotemporal Patterns in the Distribution of Albacore, Bigeye, Skipjack, and Yellowfin Tuna Species within the Exclusive Economic Zones of Tonga for the Years 2002 to 2018

The Tongan fisheries targeting the species of albacore (Thunnus alalunga), bigeye (Thunnus obesus), skipjack (Katsuwonus pelamis), and yellowfin tuna (Thunnus albacares), comprising the main tuna catch landed, within the EEZ of Tonga is critical to the economy of Tonga. Thus, it is crucial to study the spatiotemporal pattern of their catch and the influence of environmental and physical variables, in addition to the month and year of the catch. To this end, sets of eight generalized additive models were applied to model the distribution of these four species. Selection among competing models was carried out based on k-fold cross-validation, using RMSPE prediction error as a measure of model predictive performance. The following sets of predictors were considered; sea surface temperature, sea surface chlorophyll, bottom depth, month, and year. In addition, to assess the influence of fronts, gradients in SST and Chl-a were computed and used as predictors. Catch year was the most important variable for all, except Albacore tuna, for which month was the important variable. The third most important variable was SST for albacore and bigeye tuna, whereas bottom depth was the most important variable for skipjack and yellowfin tuna. A standardized index of CPUE indicates mostly inter-annual variation in CPUE for albacore and bigeye tuna, whereas a it indicates a general increase in CPUE for skipjack and yellowfin tuna. Hotspots of albacore tuna catches are around the northern and southern edges of the exclusive economic zone and typically during the months of June to August. The bigeye tuna hotspots were concentrated on the eastern side of the islands, in waters overlying trenches; this was most obvious during the months of January to June. Skipjack tuna hotspots were near the edges of the exclusive economic zone, although it is caught in smaller amounts to the three tuna species considered and higher catch rates were observed only after 2014. For yellowfin tuna, the highest catch rates were concentrated around the islands and descending towards the southern edge of the EEZ. As part of the initiative of this study to support national optimal resource management, this study generated standardized CPUE (indices of abundance), an important input in stock assessment, and also looked into the potential influence of environmental and physical variables on the CPUE of these valuable tuna stocks within the EEZ of Tonga.

Spatiotemporal physical barrier analysis of southern king crab (Lithodes santolla) catch rates in Magallanes, Chilean Patagonia (2014–2020)

Spatiotemporal patterns on fishing success and catch rates were analyzed for the southern king crab (Lithodes santolla) fishery in Chilean Patagonia (48ºS-55ºS). The analysis considered the effects of physical barriers on the spatial distribution within two complex coastal geography fishing zones. The north zone (50–54°S), close to Puerto Natales, has the more complex coastal topography, with numerous islands, archipelagos, channels, and inland sea. Instead, the south zone (55°−56°S) is relatively free of barriers. Operational data from 2014 to 2020 were obtained on board by scientific observers. The best spatiotemporal model was an opportunistic spatial pattern characterized by different yearly spatial realizations for fishing success and catch rates, with seasonal and bathymetric effects for catch rates. The higher catch rates in the north zone are probably associated with the size of crab aggregations, which tend to disperse over a wider area due to physical barriers. In contrast, the south zone has fewer physical barriers and more concentrated crab aggregations. Therefore, catch per unit effort in the southern king crab fishery should consider the effects of physical barriers on the spatial correlations and other covariables for fishing power and catchability effects.

Geo-spatial distribution and trends of trawl catch and bycatch off the south Konkan coast, Maharashtra, India

Trawl fishing is well-known for its high catch rate, but due to its non-selective nature, it is now widely acknowledged to have an impact on biodiversity and habitat. The geographical and temporal aspects of trawl catch, bycatch, discard, and ichthyofaunal trawl diversity along the south Konkan coast of Maharashtra, India, are contemplated in the current study. The data of 177 georeferenced trawl hauls, towed between 15°53’38”N to 17°34’52”N latitude and 72°54’29”E to 73°25’48”E longitude, revealed that maximum bycatch (70–110 kg/haul) and discard (60–110 kg/haul) regions were found towards the southern direction, near ecologically sensitive estuarine areas off the south Konkan coast, Maharashtra. The post and pre-monsoon seasons were found to be much more productive in terms of catches, while the post-monsoon and winter seasons had the highest species diversity 38.15% and 33.86%, respectively, with the winter season having higher discard rates. In the present study, bycatch contributed nearly 49% of the total catch, with the maximum catch per hour recorded in October (62.20 kg) and the discard per hour in January (14.59 kg). There were 134 different species of fish and shellfish recorded, and the family Carangidae (8.21%) was prominent in terms of species richness, followed by Penaeidae (6.72%), Clupeidae (5.22%), Engraulidae (5.22%), and Sciaenidae (4.48%). The results of various biodiversity indices confirmed that the studied region is blessed with rich and evenly distributed biodiversity. The mapped predictive values of trawl fishing showed a high fishing pressure zone towards the south off the Maharashtra coast, and it highlighted the need for suitable strategies for the conservation and management of fisheries resources to achieve long-term sustainability in that region.

Exploring biophysical links of catch rate from mid-water trawl fishery in the north-west coast of India, Eastern Arabian Sea: A remote sensing approach

Fish frequently shift their distribution ranges as a result of changes in preferred environmental factors. Knowledge on distribution of fish in relation to their environmental optima is crucial for improving the understanding of fishing grounds and planning sustainable exploitation. This study investigated the monthly variability in environmental factors impacting the catch rate and the spatio-temporal distribution patterns of fish along northwest coast of India (NWCI) from 2017 to 2019. The time series images of sea surface temperature (SST), sea surface height anomaly (SSHa), chlorophyll-a concentration (CHL), and euphotic depth (Zeu) indicate close coupling between bio-physical variables in the region. Generalized Additive Model (GAM) applied to the catch rate of mid-water trawlers found that CHL and Zeu were the most influential variables for ribbonfish distribution, while CHL and SST influence squid distribution and SST and SSHa influence cuttlefish distribution. The total deviation explained 37.70 %, 10.70 %, and 22.28 % in the final model for simulating the spatio-temporal distribution of ribbonfish, squid, and cuttlefish, respectively. Environmental factors were significant in the final GAM model (p < 0.05). Spatio-temporal distribution patterns of fishery resources from mid-water trawlers showed that they were related to biophysical changes in the northwest coast of India. The high catch rate was observed in the northern latitudes during the post-monsoon (October), the major fishing season in the region. However, it shrank and shifted to southern latitudes during the winter (January). This study could be adapted to nearby countries in the Arabian Sea region for an effective and useful tool to monitor and manage the fishery resources. Furthermore, it could aid in decision-making for policymakers and resource managers to formulate strategies for holistic marine fishery management and sustainable resource exploitation.

Using fishers’ local ecological knowledge for management of small-scale fisheries in data-poor regions: Comparing seasonal interview and field observation records in East Africa

Fishers, scientists and policy makers need to describe, understand and “agree on” variations in fish catches caused by exploitation and climate change for effective fisheries management. To achieve this, relevant data with sufficient spatiotemporal resolution is a necessity. In regions of the Global South, such as the Western Indian Ocean (WIO), fish catch data useful for management is scarce or non-existing. Still, the potential of local ecological knowledge to provide such information has not been fully utilised in these regions. In this study, we evaluated fishers’ local ecological knowledge (based on interviews) against detailed seasonal fish catch variability data based on catch per unit effort (CPUE) records. Because of the importance of the monsoon seasons for marine resource variability, differences in fish catches during the northeast (NE) and southeast (SE) monsoon seasons were investigated. Fishers’ perceptions generally agreed with catch data records, both showing that the NE monsoon season generally provides higher catch rates than the SE monsoon season. The fishers’ perceptions at two of the landing sites (Nyamisati and Shangani) contradict the recorded observations by showing highest fish catches during the SE monsoon season. It was clear, however, that fishers’ perceptions in these two sites focused on the most valuable target species (prawn and tuna in Nyamisati and Shangani, respectively) rather than total catches. In this particular case, fishers’ perceptions facilitated the significance of taking target species into consideration. The findings of this study highlight the importance of integrating local ecological knowledge into scientific research to help understand the complex dynamics of coastal fisheries and improve the management of data-poor fisheries.

The application of tie-down gillnet to improve the capture of blackfin flounder (Glyptocephalus stelleri) in a sustainable way

In this study, experimental fishing trials were performed to quantitatively evaluate and compare the fishing performance of trammel nets, tie-down gillnets, and single gillnets used for catching blackfin flounder. A total of eight cruises performed at depths of 100–140 m in the waters near Yangyang, Gangwon-do, Korea. Fisheries laws in Korea currently restrict the use of trammel nets due to concerns about overfishing and bycatch. Tie-down gillnets have a support line that changes their stretched height, thus increasing their catch rate, and are an attractive alternative to trammel nets or single gillnets; unmodified gillnet. Due to a lack of quantitative evaluation of their fishing performance, the performances of these three types of gillnets quantitatively compared. The number and weight of fish, particularly blackfish flounder, caught by each net under similar circumstances were compared. Our results suggest that the fishing performance of trammel nets and tie-down gillnets is much higher than that of single gillnets. Compared to single gillnets, trammel nets performed better by 2.98 times and 2.45 times, in terms of the total number and weight of fish caught, respectively, and tie-down gillnets performed better by 2.09 times and 1.97 times, respectively. In addition, the bycatch rate of tie-down gillnet for immature blackfin flounder with the total length less than 20 centimeters was similar to single gillnet; single gillnet 17.5% of immature blackfin flounder, tie-down 20% of immature blackfin flounder, trammel net 62.5% of immature blackfin flounder. Given that many flat fish such as flounders fall out of the net during the fishing process after being stuck in single gillnets, fishermen hope to use trammel nets. However, the relatively high catch rate of trammel nets likely necessitates restrictions for their use. This study suggests that tie-down gillnets are an option for sustainable fishing practice given that they perform better than single gillnet and reduce bycatch of immature blackfin flounder when compared to trammel nets.

Status of diversity, abundance and seasonal variations of gill net catches of cichlids in Lake Bosumtwi, Ghana

The cichlids in Lake Bosumtwi are under increasing pressure with a recent build-up in local fishing pressure. This study was conducted to assess the status and seasonal catch rates of fish species using gillnets over a two-year period. Four species and one introduced fish belonging to the Cichlidae family were encountered in the study. Coptodon discolor (Günther, 1903) was the most abundant species, making up 75.5% of the total fish caught (100.1 kg). Tilapia busumana (Günther, 1903) was the least abundant species, representing only 0.6% of biomass. Catch per unit effort was significantly affected by seasonality; however, species diversity, richness and evenness were not influenced by seasonal variations. The highest catch rates (975.62 g net−1 night−1) were recorded in the minor wet season (August to November). No statistical differences were detected in the diversity indices estimated for all three seasons of study. The key physico-chemical parameters (conductivity, salinity, temperature and pH) measured were within the tolerance range for tilapia survival and growth, with the exception of dissolved oxygen that decreased below 3 mg l−1 during the lake’s deep mixing events in August. Overall, physico-chemical factors explained 75% of fish catches, with salinity levels correlating significantly with catch per unit effort.

Intra‐Annual Variability of Common Carp and Bigmouth Buffalo Electrofishing Data in Shallow Lakes

AbstractCommon Carp Cyprinus carpio and Bigmouth Buffalo Ictiobus cyprinellus are widespread across the Midwest, where they can achieve high population densities in shallow lakes. Despite their contrasting statuses as invasive and native fishes, these species are commonly managed together due to their capacity to have deleterious effects on water quality. However, intra‐annual sampling variability is poorly understood for both species, making it difficult to track population changes. We compared boat electrofishing CPUE and proportional size distribution (PSD) of Common Carp and Bigmouth Buffalo during May–October 2018–2020 in seven shallow northwestern Iowa lakes. We also estimated sampling effort necessary to reach targets of fish captured (100) and precision (relative standard error &lt; 25%) and to detect 25% and 50% differences in CPUE between samples. Common Carp CPUE peaked in June (29 fish/h), declined across the summer, and was lowest in October (9 fish/h). Bigmouth Buffalo CPUE exhibited bimodal peaks in May (16 fish/h) and October (12 fish/h), with low catches during August (2 fish/h). Common Carp size structure was largest during October (PSD of preferred‐size fish [PSD‐P] = 92) and smallest in July (PSD‐P = 58). Bigmouth Buffalo size structure was smaller in June (PSD‐P = 20) than in all other months (PSD‐P = 34). Our targets for number of fish captured and precision were typically reached within twenty‐five 15‐min electrofishing transects for Common Carp during periods of high catch rates but were not reached after 100 transects for Bigmouth Buffalo in most cases. Our results suggest that timing of sampling is important for reliably and efficiently assessing Common Carp and Bigmouth Buffalo populations. We recommend the sampling of Common Carp with electrofishing during June and the sampling of Bigmouth Buffalo during May in Midwestern shallow lakes to maximize catch rates while minimizing the influence of seasonal sampling variability.

Avoiding grey seal depredation in the Baltic Sea while increasing catch rates of cod

The escalating conflict between gillnet fisheries and the growing seal populations in Baltic Sea has increased the need to reduce direct effects in form of reduced or damaged catches. This study describes the design and catch rates of 20 different seal safe cod (Gadus morhua) pot designs suitable for the Baltic Sea. Catches in numbers of individuals and total catch weight were recorded in 2762 pot hauls with pots varying in terms of size, shape, number of entrances, entrance length, pot placement in relation to the sea floor and catch holding chamber. The aim was to investigate the how the different designs and soak times affected the catch rates under similar conditions. Volume and soak time was significantly positively correlated with catch rates and round bottom-standing pots with a fish holding chamber, funnels and 5 entrances had the highest catch rates. The findings are important for the development of cod pots, which can allow the fishers to continue fishing in areas of high seal density with static gear and hence low-carbon emission and minimum bycatch of marine mammals and sea birds.

Status of Sea Cucumber Fisheries in Mindanao: Harnessing Local Knowledge in Determining Diversity and Production Values

Sea cucumber fishery is a significant livelihood in the Philippines; however, overexploitation and inadequate management programs resulted in the decline of various sea cucumber species. This paper describes the current sea cucumber fisheries across 32 municipalities in Mindanao assessed from August 2019 to January 2020 through key informant surveys (KIS) and focus group discussions (FGD). About 47 sea cucumbers were identified from KIS, mostly for export. The high-value Holothuria scabra is the most exploited species across Mindanao, but the top catches are mainly composed of low to medium-value species. At least four sea cucumber species were noted by gatherers to have disappeared from some sites during the KIS. The FGDs showed that the sea cucumber fishery is small-scale, involving about 1,922 gatherers from 10 municipalities. Half of them (56%) engage in full-time sea cucumber gathering and employ various methods depending on the location of their collection grounds. Estimates of mean daily sea cucumber catch ranged from 1–7.3 kg-1 gatherer-1 day-1, with the highest catch in Olutanga, Zamboanga Sibugay, and lowest in Laguindingan, Misamis Oriental. Catch per unit effort ranged from 0.2-1.8 kg-1 gatherer-1 day-1, with the highest catch rate in Dimataling, Zamboanga del Sur, and lowest in Laguindingan. Gatherers often sold their catches as fresh to consolidators or traders. Net incomes from the combined fresh catches ranged from PHP 70–950, with the highest income in Olutanga and the lowest in Laguindingan. Historical trendlines show decreasing catches in all sites over time. Overall, the sea cucumber fishery in Mindanao is rapidly declining and needs urgent management interventions to sustain stocks and livelihoods.

Catch-and-Release Angling Effects on Lake Sturgeon in Wisconsin, USA

Abstract Discard mortality is an important factor to consider when managing catch-and-release fisheries. Even low levels of discard mortality can induce population-level effects particularly in long-lived, low-productivity species like Lake Sturgeon Acipenser fulvescens. Unfortunately, little is known about the effects of catch-and-release angling on Lake Sturgeon physiology and probability of discard mortality. We used controlled angling events with standardized gear to capture 96 Lake Sturgeon from August to October 2019 from four regional locations in Wisconsin, USA. We evaluated the physiological effects of angling and activation of the stress response using whole blood concentrations of lactate and glucose as well as assessment of reflex impairment and postcapture monitoring of recovery time. Lactate levels were positively related to fight duration and the fight duration × total length interaction. Glucose level was related to the time a fish spent out of water postangling event. Water temperature had a positive effect on the probability of reflex impairment and the probability that a sturgeon required recovery time. The recovery duration was positively related to the amount of time that the fish was out of water. The movements of a subset of 15 individuals from one location were monitored using acoustic telemetry for approximately 2 weeks postangling. All individuals showed continuous up- and downstream movement during the postrelease monitoring period, and there was no evidence of mortality related to the angling events. Managers considering catch-and-release fisheries for Lake Sturgeon should consider population-specific relative abundance and catch rates. They should exercise caution in scenarios when seasonal aggregations may lead populations to be susceptible to high catch rates, during times of elevated water temperatures, or the combination of these factors. The Lake Sturgeon in this study appeared to be robust to angling-induced stress effects. Nevertheless, caution is still warranted, as low levels of discard mortality have the potential to influence low-productivity species like Lake Sturgeon.

How catch uncertainty and harvest regulations drive anglers’ choice for pike (Esox lucius) fishing in the Baltic Sea

In the brackish lagoons located in coastal inshore areas around the German island of Rügen, pike Esox lucius is a highly sought after target species for recreational fishers. Yet, the pike stock is currently in decline, and conflicts with other user groups (specifically commercial fishers) have emerged. To inform future fisheries management, an improved understanding of the human dimensions of recreational fishers, including their preferences for catch outcomes and regulations, is relevant. Our objective was to better understand how German recreational pike fishers react to different types of harvest regulations in trade-off with risky or ambiguous catch outcomes for pike and other predators in the lagoon fishery. We conducted an online survey including choice experiments for angling experiences that differed in seven attributes. Data were analyzed using a latent class model. We found four distinct angler types differentiating resident and tourists and dependency on pike. Specifically, we identified a highly involved pike tourist (42 % average probability), a consumptive, generalist tourist angler type (18 %), a highly specialized local trophy pike angler type that readily engaged in catch-and-release (12 %), and a local generalist angler that also benefitted from the catch of other predators than pike (18 %). Despite heterogeneity in preferences, all four angler types generally accepted more restrictive regulations for pike removals than currently in place, and dispreferred low catch probabilities compared to catch ambiguity. Most angler types also revealed diminishing marginal utility returns for catch rates, where the first three pike in a day provide utility, while the marginal benefits of catch rate decrease to zero for more than three pike per day. Angler types varied more in their preferences for trophy pike, the general attractiveness of the pike as a target and the utility derived from catching fish other than pike. Particularly the more specialized angler types focused on size rather than catch rate. Despite preference heterogeneity, focusing management attention on maintaining a sufficiently high catch rate and increasing the number of trophy pike in the stock seems to satisfy the expectations of most angler types. To achieve such outcomes, the anglers of all types would overwhelmingly support implementing harvest slots of 50–85 cm that allow both small and large fish to be released (rather than the current minimum-length limit of 50 cm), and accept reductions in the daily bag limit to 1 pike per day (relative to the current of 3 pike per day). Implementing these policy measures would unlikely generate substantial conflict with anglers represented in our survey.