Commercial Catch Research Articles

Length–weight relationships of 12 marine fish species from the Pacific coast of Guatemala associated with small‐scale fisheries

The length–weight relationships (LWRs) were estimated for 12 fish species. The species were collected monthly from the commercial catch of small-scale fisheries using gillnets (mesh size 7.6–15.2 cm, length 200–1,000 m, 6–48 hr of operation during the day) and longlines (surface and bottom, 300 hooks, sardine bait, operation during the day) in the period October 2017 to July 2018 along the Pacific coast of Guatemala. Most values for the parameter (b) of the length-weight equations were within the commonly expected range (2.50–3.50) except for two species: Bagre pinnimaculatus (2.22) and Menticirrhus panamensis (3.56). All values for the coefficient of determination (r2) were above .95 and thus the estimates can be considered reliable. Besides novel LWRs we provide for some species estimates which include a new TLmax not yet involved of any LWR studies.

THE CURRENT STATE OF THE KEFAL FAMILY (MUGILIDAE) IN THE COASTAL ZONE OF THE DAGHESTAN COAST OF THE CASPIAN SEA

For more than a century of active commercial exploitation and environmental changes in the Caspian Sea, the structure of the population of marine fish species has undergone significant qualitative and quantitative changes. In this group of fish until 1960, the main role in the fishery was played by sea herring, which provided up to 50–70% of the total fish catch in the region. Interest in the study of marine fish of the Caspian Sea, using the example of mullets, Black Sea acclimatizers, is due to the fact that under new conditions, as well as a result of deep negative changes in the ecology of this reservoir under the influence of natural and anthropogenic factors, especially recently. At present, among marine fish, one of the main and promising fishing objects is mullet, which, since the period of acclimatization, has formed a high abundance in the coastal zone of the Daghestan coast of the Caspian Sea. Mullet are euryhaline fish that can live both in sea, salty water, and freshwater bodies. In this regard, the objects of this study were mullet (singil), the study of their commercial catches and stocks in the Caspian Sea.

Trawl-induced biological and chemical degradation in Bengal Offshore

Coastal and estuarine area of West Bengal offshore in India enjoys the world’s largest mangrove food web named ‘Sundarbans’ declared as the World Heritage Site in 1989, which exhibits excellent breeding ground of uncountable fish and other marine species. Growing population has forced intensification of trawl netting by commercial fishermen all along the offshore during the last few decades. This paper presents a case study of Shankarpur–Digha–Petua fishing zone where modern bull trawlers continuously drag bigger trawl nets through ocean bottom and obtain huge commercial catch destroying at random under-sea habitat of many non-economic but ecologically valuable marine species. Trawling has been proved to destroy many ecologically worthy juveniles occupying the primary and secondary trophic levels of marine food chain. Anthropogenic malpractice seems to have created a great food crisis for all predators including apex species like shark, dolphin, and seal whose sustenance is suspected to be at stake leaving seafood-dependent coastal fishing population as the worst sufferer. Thus, economic profit is gained at the cost of undesired ecological loss. An effective Environmental Management Plan is also discussed here which will help keeping balance between ecology and economy to ensure conservative use of marine resources towards sustainable development of the ecology of this World Heritage Site.

The comeback of Atlantic bluefin tuna (Thunnus thynnus) to Norwegian waters

We document that Atlantic bluefin tuna (BFT) began making a comeback from 2012 onwards into Norwegian waters, after several decades of absence, in parallel with an overall increased abundance recorded for eastern BFT. This study explores the distribution, biology and ecology of BFT reestablishing in Norwegian waters. We analyzed commercial catch and bycatch data including biological data on weight, length and age of BFT from 2016–2018. Predominantly larger (overall range in catches: 120−465 kg in weight and 184−297 cm in straight fork length (SFL)) adult individuals between 6 and 14 years old have recently started to revisit Norwegian waters. Numerous recently documented BFT observations were reported in this study, and a significant increase was detected from 2012 (n = 1) to 2018 (n = 105) (p < 0.01). Schools of BFT were observed predominantly from June to December, including the northernmost registered observation in history recorded at 76.2 °N in September 2018. Atlantic bluefin tuna has now reestablished and has shown a positive comeback to its historical migration patterns in Norwegian waters, where it has expanded its feeding areas towards the north.

History and status of sturgeon stock (Acipenseridae) in the Caspian pool

Analysis of materials from long-term studies characterizing the current state of sturgeon stocks in the Volga-Caspian fisheries basin, and the dynamics of commercial catches of beluga, sturgeon and stellate sturgeon in the XX - XXI centuries indicates that the Northern Caspian occupies the leading value in catch volumes, where more than 70 % of sturgeon fish are annually harvested. In the first half of the twentieth century sturgeon stocks were determined by the scale of natural reproduction in rivers and fishing volumes; in the second half, natural and anthropogenic factors began to intensively influence the formation of sturgeon stocks. The development of hydraulic construction on rivers, an increase in the withdrawal of freshwater runoff, a decrease in sea level to -29.0 mBS, pollution by industrial and agricultural runoff have necessitated the development of a set of measures for the reproduction, conservation and rational use of the Caspian’s aquatic biological resources. As a result of the studies, the response of the sturgeons to the changed conditions of reproduction has been determined in order to restore and increase their commercial stocks; high ecological adaptability of sturgeons to various living conditions within their range, their exceptional plasticity and pronounced intraspecific differentiation have been established. These indicators point to the possibility of creating conditions that meet the requirements for water quality for the life of sturgeons during migration and reproduction. In the course of the analysis of the obtained data, the influence of regulation of the Volga River flow on the efficiency of natural reproduction of sturgeons has been evaluated; the role of industrial sturgeon breeding in sturgeon stock formation has been shown; the abundance of juveniles in the North Caspian and adult individuals on feeding pastures of the sea has been estimated; trends in the number of sturgeon producers migrating in the Volga to spawning sites have been identified; the prospects for the restoration and rational use of sturgeons in the Volga-Caspian basin have been determined.

Small Pelagic Fish Value Chain and Its Contribution to Local Food Security: A Case Study in &lt;em&gt;Gandara&lt;/em&gt; Fishing Village in Southern Coast of Sri Lanka

The small pelagic fishery has a critical importance both in terms of economic and food security concerns for coastal communities around the world. This study aimed at investigating the domestic fish value chain along with key economic agents, their roles and functions and to assess the contribution of the value chain to the local food security. In-depth interviews were conducted with at least five agents at each node of the value chain, and they were selected through stratified purposive and snowball sampling. Six different marketing channels were identified from fishers to consumers. Fishers are the primary producers. Local wholesalers played a conclusive role as the major middlemen, commission agents and moneylenders. Regional suppliers transported fish from landing sites to the wholesalers of other regional markets. The retail market consisted of mobile fish vendors and local retailers. Ninety-eight percent of the commercial catch reached the consumer, with only 2% waste or by-usage. Seventy percent of that commercial catch directly moved to the local consumers along three marketing channels. The prominent channel was “Fisher-Retailer-Consumer” (37%). This value chain had a significant contribution to local food security in terms of availability, accessibility, utilization and stability. The consumer price was affected by the number of intermediaries involved in the chain. Less number of intermediaries along the chain will improve the local food security while ensuring an affordable price for the consumers. Local consumers prefer fresh fish which hinders the desire of value creation in domestic value chains.

Fishing for an institution-based first-mover advantage: The Norwegian snow crab case

When the first Norwegian commercial catch of snow crabs was taken in the Barents Sea in 2012, an unexpected opportunity arose to create a new, profitable natural resource-based industry. However, hidden under the surface were massive biological, technological, and institutional uncertainties. This study first explores what motivated the entrepreneurs to invest in an industry exposed to extreme uncertainty and which firm and vessel resources were necessary to operate. The findings uncovered that most of the entrepreneurs had already exited another fishery with a profit. Thus, they were looking for new attractive business opportunities where they could apply resources and capabilities already accumulated. Furthermore, this study asks if there have been any survival-threatening challenges so far in the industry. The findings show that increased competition and the Russians closing the Loophole dramatically changed the opportunities for profitable fishing. Finally, the study discusses whether the players have the potential to gain a sustained institution-based first-mover advantage (FMA), i.e., a gratis fishing quota. It is argued that the snow crab vessels have positioned themselves into a historical stream of events, which can, at best, give rise to a gratis institutional protection of a valuable natural resource. Thus, if the vessels are allocated free individual transferable quotas, they will secure a sustained FMA, as a similar event is unlikely to occur in the future. Finally, in the paper, findings and implications are discussed.

Connecting Crabs, Currents, and Coastal Communities: Examining the Impacts of Changing Ocean Conditions on the Distribution of U.S. West Coast Dungeness Crab Commercial Catch

Dungeness crab (Cancer magister) is one of the most lucrative fisheries on the U.S. west coast. There have been large spatial and temporal fluctuations in catch, which reflect the interconnected influences of the coupled natural-human fishery system. Changing ocean conditions are likely to further alter the magnitude and distribution of Dungeness crab catch, the impacts of which will propagate ecologically and through the social systems of fishing communities. Therefore, the effect of changing ocean conditions on U.S. west coast Dungeness crab catch per unit effort (CPUE) was used as an interdisciplinary case study to examine the susceptibility, a metric that integrates Dungeness crab reliance and social vulnerability indices, of coastal communities to changes in the fishery. Statistical models indicated that ocean conditions influence commercial CPUE three to five years later and that CPUE is likely to decline in the future as ocean conditions change. In particular, sea surface temperature scenarios for 2080 (+1.7 °C and +2.8 °C) reduced Dungeness crab CPUE by 30-100%, depending on fishing port latitude. Declines in Dungeness crab CPUE were greater for southern port communities than for northern port communities under both scenarios – demonstrating greater exposure at the southern end of the species range. We show that U.S. west coast communities are differentially susceptible to a decline in Dungeness crab catch, with Washington communities being at least five times more susceptible than California communities. Our overall assessment showed varying levels of risk (a combination of exposure and susceptibility) for Dungeness crab fishing ports that do not necessarily align with regional or fishery management boundaries.

How do environmental factors affect the yield of European eel (Anguilla anguilla) in a restocked population?

Restocking of European eel (Anguilla anguilla) is a widespread practice throughout Europe. Conditions during restocking activities and mortality related to restocking practices have been discussed, however, factors affecting these restocked populations afterwards are mostly not considered. In this study we used a machine learning method followed by generalized linear model to analyze long time eel restocking, commercial fishery and environmental data from Lake Võrtsjärv, Estonia, to detect whether significant relationships exist within these data. It was found that environmental parameters can have an effect on the commercial eel yield both retrospectively and during the particular fishing year. Considering that 7-year old eel was the most common age group in commercial catch, we introduced a 7-year gap between eel restocking and yield to study the most important abiotic and biotic factors during the first year of eel restocking that have an effect on the yield. According to our results, cyanobacterial biomass and summer water temperature during the year of restocking had the strongest negative impact on the yield 7 years after, while the number of restocked individuals and copepod biomass had a positive effect. During particular fishing year, however, the yield was most notably positively affected by total phosphorous concentration, number of individuals restocked 7 years before and metazooplankton biomass in the lake.

Fishing as an important source of food in the Arctic and subarctic zones of Yakutia

Abstract The peculiarity of natural conditions of Yakutia plays an important role in the formation of economic activities of its population. A significant number of rivers and lakes are a favorable condition for the development and preservation of traditional fishing. Currently, more than 89% of the commercial fish catch is produced in the lower reaches of the large northern rivers and lakes in the Arctic and subarctic zones of Yakutia. The main part of this catch is whitefish species, which are valued for their fat content, protein content, culinary, and taste qualities. Fish is a valuable food product for the population of Yakutia. This article presents the results of the study on the nutritional value and the content of heavy metals in the Arctic cisco meat. The high content of fat and protein in the studied samples shows that the Arctic cisco meat belongs to high-protein and high-calorie products and has a high biological value. It was found that on average, the level of toxic metals in the Arctic cisco meat does not exceed the norms accepted in Russia for fish products. The data obtained suggest that the content of heavy metals in fish is due to the peculiarities of living conditions and environmental pollution. Over the past decades, the volume of fish production in Yakutia has been declining due to the socioeconomic and climatic factors. Due to the anthropogenic pollution of water in rivers and lakes by oil products and effluents and waste from various sectors of the economy, especially the mining industry, there is a reduction in the fish resources and there is a need to monitor the environmental condition of the fishing reservoirs and the fish food quality.

Elasmobranch bycatch by prawn trawls in the Gulf of California: First comprehensive analysis and the effect of fish escape devices

We report results from the first detailed investigation of elasmobranch bycatch that contains data on species, sex, and length-frequency distributions of animals collected in the coastal south-eastern and entrance region of the Gulf of California. Using data from fishery-independent prawn trawl surveys between 2011–17, we found differences between years and zones in the number of species per tow in summer when more samples were taken, but we did not find differences in autumn and winter. We present size-frequency distributions with size at first maturity for Urobatis halleri, Urotrygon chilensis, Rhinoptera steindachneri, Hypanus dipterurus, Gymnura marmorata, and Pseudobatos glaucostigmus, which were the species most frequently present in the prawn trawls during the surveys. These distributions are presented by zone, depth stratum, and season (mainly summer, when commercial prawn trawling is prohibited, and thus information from commercial catches is not available). We found significant differences in the mean size between mature females and mature males for five of these six species. We also found that fish escape devices installed in the prawn nets early in 2016 improved the escape of mid-sized rays, demonstrating size selectivity of the fishery and suggesting the potential to improve further the escape of large-sized rays by modifying fish escape devices. Furthermore, the large number of rays caught (21 species) compared with the number of sharks caught (four species) suggests much lower catchabilities for sharks than for rays in demersal prawn trawl gear.

Fishery management and spatial variation of giant clam stocks: lessons from New Caledonia

Giant clams have been over-exploited throughout their wide geographical range in the Indo-Pacific. Marine reserves could be one tool to potentially safeguard broodstock, but their effect on giant clam abundance and the differential benefits of lagoon reserves compared to barrier reef reserves is still unclear. We assessed abundances of four species of giant clams across 20 barrier reef and 30 lagoon reef sites across 600 km of coastline in New Caledonia using stratified underwater visual censuses. Tridacna maxima was the most common species. T. derasa was significantly more abundant in marine reserves than at sites open to fishing, but there was no effect of marine reserves on total abundance pooled across the four species. T. squamosa was significantly more abundant on barrier reefs, while Hippopus hippopus was found solely on lagoon reefs. National data from fisher logbooks shows a marked reduction in commercial catches of giant clam following implementation of daily catch limits of 5 giant clams per vessel per trip. Despite small daily bag limits of 2 giant clams per recreational fisher per trip, the recreational catch appears to be significant and much greater than the commercial catch. The utility of marine reserves on giant clams appears to be species specific, and might be diminished for the group as a whole by the concomitant protection of their natural predators. Both lagoon and barrier reef sites should be included in reserve networks. Our data suggest that daily boat/trip limits are an effective output control, at least for commercial fishers, but might not safeguard giant clams if recreational fishers are numerous. Further fishery restrictions on the less common species might be needed to ensure their persistence in the Indo-Pacific.

THE IMPACT OF ENVIRONMENTAL CHANGES ON BLACK MARLIN, Makaira indica (Cuvier, 1832) ABUNDANCES IN THE EASTERN INDIAN OCEAN

Black marlin (Makaira indica) is commonly caught as frozen by-catch from Indonesian tuna longline fleets. Its contribution estimated 18% (~2,500 tons) from total catch in Indian Ocean. Relative abundance indices as calculated based on commercial catches are the input data for several to run stock assessment analyses that provide models to gather information useful information for decision making and fishery management, however, little are known about the influence of environmental factors to its abundance. In this paper, the abundance was represented as standardized index in order to eliminate any bias on other factors which might influence it. Data were collected from August 2005 to December 2017 through scientific observer program (2005-2017) and national observer program (2016-2017). Most of the vessels monitored were based in Benoa Port, Bali. Overall, time trends of abundance was fluctuated, although, there was increasing trend since 2010 then dropped significantly into relatively similar figure in 2005. Even though, Sea Surface Temperature (SST) and Sea Surface Height (SSH) were statistically significant when incorporating into the models, but it allegedly wasn’t the main driver in determining the abundance of black marlin. Instead, it was more likely driven by spatio-temporal factors (year and area) effect rather than environmental changes.

Describing historical habitat use of a native fish-Cisco (Coregonus artedi)-in Lake Michigan between 1930 and 1932.

With the global-scale loss of biodiversity, current restoration programs have been often required as part of conservation plans for species richness and ecosystem integrity. The restoration of pelagic-oriented cisco (Coregonus artedi) has been an interest of Lake Michigan managers because it may increase the diversity and resilience of the fish assemblages and conserve the integrity of the ecosystems in a changing environment. To inform restoration, we described historical habitat use of cisco by analyzing a unique fishery-independent dataset collected in 1930-1932 by the U.S. Bureau of Fisheries' first research vessel Fulmar and a commercial catch dataset reported by the State of Michigan in the same period, both based on gear fished on the bottom. Our results confirmed that the two major embayments, Green Bay and Grand Traverse Bay, were important habitats for cisco and suggest that the Bays were capable of supporting cisco to complete its entire life cycle in the early 20th century as there was no lack of summer feeding and fall spawning habitats. Seasonally, our results showed that cisco stayed in nearshore waters in spring, migrated to offshore waters in summer, and then migrated back to nearshore waters in fall. The results also suggest that in summer, most ciscoes were in waters with bottom depths of 20-70 m, but the highest cisco density occurred in waters with a bottom depth around 40 m. We highlight the importance of embayment habitats to cisco restoration and the seasonal migration pattern of cisco identified in this study, which suggests that a restored cisco population can diversify the food web by occupying different habitats from the exotic fishes that now dominate the pelagic waters of Lake Michigan.

Feasibility of targeted fishing in mesoscale oceanic eddies: a study from commercial fishing grounds of Andaman and Nicobar Islands, India

ABSTRACT Mesoscale eddies are important ocean phenomena that enhance biological productivity by mixing of water column and influence fishery catches, especially in stratified seas such as Bay of Bengal and Andaman Sea. The current study was conducted around the Andaman and Nicobar Islands (ANI), India located in the Eastern Indian Ocean. The study tested the feasibility of targeted fishing in eddies, by characterizing the mesoscale eddies in the region, towards developing operational altimetry-based fishery advisories for the fishers. We analysed fish catch data from 15,370 commercial fishing trips from the Islands using five fishing gears during 2014–17 spatially vis-à-vis the eddies delineated from Maps of Sea Level Anomaly (M-SLA). We show that 5-24% of the routine commercial catches occurred in eddies, fishery catches are positively influenced by different eddy zones and the fish catch using different fishing gear are significantly higher in some of the eddy zones. We generated experimental advisories showing locations of eddies and their zones, identified using Near Real-Time M-SLA data and guided the commercial fishers for targeted fishing in eddies. The fish Catch Per Unit Effort (CPUE) from the experimental fishing within the eddy zones was significantly (p < 0.01) higher than that from the traditional fishing grounds in the non-eddy areas. The spatio-temporal analysis of eddies around ANI during 2009–16 showed the occurrence of higher number of anticyclonic eddies, majority of which move westward and have a lifespan of less than 2 weeks and amplitude less than 4 cm. In the current study, the areas around ANI with frequent eddy occurrence and eddy density have been identified, which could aid in increasing the fishing intensity by targeting the pelagic fishes, using longlines, gillnets and ringnets. Thus, we show the possibility of using eddy fishing advisories generated from altimeter data, for augmenting the currently operational Potential Fishing Zone (PFZ) advisories that are generated using optical/thermal remote sensing data and disseminated to the coastal fishers in India. This will be helpful especially for the regions with and during periods of persistent cloud cover.

Highly resolved spatiotemporal simulations for exploring mixed fishery dynamics

To understand how data resolution impacts inference on mixed fisheries interactions we developed a highly resolved spatiotemporal discrete-event simulation model MixFishSim incorporating: i) delay-difference population dynamics, ii) population movement using Gaussian Random Fields to simulate patchy, heterogeneously distributed and moving fish populations, and iii) fishery dynamics for multiple fleet characteristics based on population targeting under an explore-exploit strategy. We applied MixFishSim to infer community structure when using data generated from: commercial catch, a fixed-site sampling survey design and the true (simulated) underlying populations. In doing so we thereby establish the potential limitations of fishery-dependent data in providing a robust characterisation of spatiotemporal distributions. Different spatial patterns were evident and the effectiveness of a simulated spatial closure was reduced when data were aggregated across larger spatial areas. The simulated area closure showed that aggregation across time periods has less of a negative impact on the closure success than aggregation over space. While not as effective as when based on the true population, closures based on high catch rates observed in commercial data were still able to reduce fishing on a protected species. Our framework allows users to explore the assumptions in modelling observational data and evaluate the underlying dynamics of such approaches at fine spatial and temporal resolutions. From our application we conclude that commercial data, while containing bias, provides a useful tool for managing catches in mixed fisheries if applied at the correct spatiotemporal scale.

Efficacy of restocking an estuarine-resident species demonstrated by long-term monitoring of cultured fish with alizarin complexone-stained otoliths. A case study

Long-term monitoring data and models have been used to explore the efficacy of restocking an estuarine-resident teleost species. Juveniles of Acanthopagrus butcheri were cultured from broodstock from the Blackwood River Estuary in 2002 and their otoliths stained with alizarin complexone. 150,000 marked juveniles were released into the Blackwood River Estuary at three months old in early 2003, with the stain in their otoliths subsequently remaining visible during the following 16 years. Samples of A. butcheri were obtained annually from a commercial gill net fisher and at intervals by fishery-independent methods. Commercial catch per unit effort was positively related to freshwater discharge. Indices of year class strength, derived from annual age-frequency distributions and assuming length-dependent natural mortality, demonstrate that between 1993 and 2012, natural recruitment to the population was only strong in 1999 and 2008 and was not significantly related to freshwater flow. The number of wild stock A. butcheri ≥ minimum legal length (250 mm total length), comprising mainly the 1999 year class, were estimated to have declined sequentially to only ∼12,000 fish in 2010. The restocked fish contributed between 61 and 73 % to the total number of fish in the commercial catches between 2007 and 2010 and their numbers remained at > 10 % of their number at release until 2011. The contribution of the 2008 year class, of which ∼50 % had been estimated as derived from restocked fish, increased from 20 % of the commercial catch in 2012 to between 50 and 80 % between 2013 and 2018. A progressive decline in growth of year-class groups of wild stock fish, from 1970-1998 to 2008-2011, is considered to reflect the detrimental effects of hypoxia. Restocked fish grew less rapidly than younger and older year-class groups of wild stock fish, suggesting that the growth of cultured fish may have been compromised by hatchery processes. The large contributions made by restocked fish to commercial catches over several years and to future generations highlight the efficacy of restocking for replenishing and sustaining a depleted population of an estuarine-resident species.

Diversity, abundance and size structure of fishes and invertebrates captured by an intertidal fishing weir at Bramber, Minas Basin, Nova Scotia

Capturing fish using a weir or trap on the intertidal flats of the Bay of Fundy was developed by native Mi’kamaq who later taught the method to the European settlers. Between 1800-1910 fish weirs were a significant part of the important American shad fishery in the inner Bay of Fundy before the collapse of the northwest Atlantic population from pollution and damming of major spawning rivers in the United States. Weirs remain an important segment of the Minas Basin fisheries but now the largest commercial catches consist of Atlantic herring, gaspereau and flounders. Studies on the fishes captured in Minas Basin weirs were published in 1852, 1924, 1984 and 2014, but all lacked a sampling intensity which would fully describe the diversity, abundance and size structure of the catch. An intertidal weir at Bramber, Minas Basin was surveyed during April-July, 2017 where catches were examined at each low tide. The weir was constructed on the intertidal flat during early April after Minas Basin cleared of drift ice. During the study period mean daily tide range was 10.46 m with a maximum spring tide range of 13.72 m. A total of eight neap and eight spring tide cycles were observed. Daily water temperature of Minas Basin was 8.0 C° during late May and increased to a maximum of 21.4 C° in late July. Fish and invertebrate collections began on April 10 and continued daily until July 22 when water temperatures in the trap became too warm for by-catch species to survive (+25 C°). During the study period an estimated total of 674,402 fishes consisting of 45 species were captured and of these 57,950 were measured. The most abundant fishes observed were gaspereau (alewife and blueback herring 51.9%), rainbow smelt (13.9%), Atlantic herring (13.0%) and tomcod (10.1%). Other commonly captured fishes were American shad, skate (little and winter), winter flounder, windowpane flounder, striped bass, mackerel and Atlantic sturgeon. A total of 18,511 invertebrates were captured and counted. The most abundant were long-fin squid (13.8%) and crustaceans (rock crab, lady crab; 84.0%). Keywords: Bay of Fundy; Canada; Clupeidae; commercial fishing; temperatures; tides

Growth and mortality parameters of Caspian kutum, Rutilus kutum, in southern Caspian Sea

The Caspian Kutum , Rutilus frisii , is one of the endemic and most important commercial cyprinid species in the southern Caspian Sea. A detailed study on growth and mortality parameters of this species was conducted based on 700 samples collected from commercial catches of beach seining in Guilan and Mazanderan provinces during fishing season 2017-2018. Females were dominated in both studied populations. Size frequency distributions showed significant variation among same sexes and between different sexes. The different WLRs were observed, positive allometric in Mazanderan, and negative allometric in Guilan. There were significant differences in growth parameters between sexes, females were of much greater asymptotic length than males, while the male fish had a higher growth rate and attained a smaller theoretical L ∞ size than females. The theoretical maximum length ( L ∞ ) was larger than the maximum one recorded during sampling. Based on the Bhattacharya method, the Caspian kutum from Guilan fishing grounds was more diverse, and included nine cohorts, while the population from Mazanderan Province showed only six cohorts. The linearized catch curve based on age composition data showed that total mortality rates ( Z ) are 1.32 year -1 and 0.63 year -1 for males and females of Guilan, respectively, that of males in Mazanderan is 1.04 year -1 and of females 0.86 year -1 . The natural mortality rates ( M ) were 0.48 year -1 for males and 0.26 year -1 females in Guilan, and was found to be as 0.26 year -1 and 0.45 year -1 for males and females of Caspian kutum caught in Mazanderan. The exploitation ratio ( E ) was found to be higher than 0.5 for both sexes from Guilan, and to be lower than the expected optimum level of exploitation in Caspian kutum males and females caught in Mazanderan.

The influence of rainfall on recruitment success and commercial catch for the large sciaenid, Argyrosomus japonicus, in eastern Australia

Freshwater flows into estuaries influence fish populations through effects on recruitment, growth and mortality. We compared year class strength of a large sciaenid Argyrosomus japonicus with rainfall through a 16-year period in southeastern Australia, to understand the influence of freshwater input on this estuary-dependent and depleted population. Relative year class strength, estimated by back-calculating age composition data from commercial fishery landings, was positively related to rainfall within estuarine catchments (R2 = 52%). Commercial estuarine landings from a separate 29-year dataset were positively related to rainfall two and three years earlier (R2 = 21% and 44%, respectively). Year class strength of a key prey species, the penaeid prawn Metapenaeus macleayi, was also related to year class strength of A. japonicus (R2 = 39%), suggesting that rainfall influences recruitment of A. japonicus by affecting food availability. Several years of above average rainfall may be required to promote recruitment substantial enough to rebuild the population.