Commercial Landings Data Research Articles

Larval presence and settlement of the American lobster (Homarus americanus) in a changing southern New England estuary

During the late 1980s and early 1990s, the American lobster (Homarus americanus) fishery boomed in southern New England, but starting in the early 2000s lobsters declined in the nearshore regions and the fishery retracted. While previous research has focused on the causes for the declining numbers of adult lobsters in the region as well as lobster settlement, lobster larvae were not sampled in Rhode Island waters. Additionally research was mixed on the origin of lobster larvae found inshore. To examine larval presence in coastal Rhode Island, weekly net tows were conducted at the mouth of Narragansett Bay during summer from 2019 to 2021, and light traps were deployed in 2020 and 2021. Time series segmentation and generalized linear models assessed trends and connections between lobsters caught in trawl surveys, commercial landings data, lobster settlement data, bottom water temperatures, and climate indices. Larval supply to Narragansett Bay is very low and mostly concentrated in the East Passage where ocean water flows into the bay, suggesting that a failure in larval supply from offshore sources is harming local population levels. Time series segmentation and models indicate that declines in lobster settlement followed the decline in adult lobsters in coastal Rhode Island, not Narragansett Bay. Altogether, the data suggest that larval lobster are transported inshore from spawning stock outside the bay. Present circulation patterns combined with the movement of lobsters into deeper waters has made the transport of larvae to Narragansett Bay unlikely.

Costly crustaceans: A hedonic price analysis of the Florida stone crab

The stone crab (Menippe mercenaria and Menippe adina) fishery is the second most valuable commercial fishery in the state of Florida, with $30 million in dockside annual landings in 2019, It is a unique fishery in that only the claws are harvested, and the crab is returned to the sea where a high portion of them survive. There is substantial variability in the ex-vessel prices paid to fishers for stone crab claws, with claws yielding from $5 to over $30 per pound. However, there is limited knowledge with respect to what influences the prices of this valuable seafood product. Hedonic models allowed us to estimate the effect that different product attributes of a harvested stone crab claw have on the price. Here, we used commercial landings data from 2009 to 2020 to investigate the impact of attributes including claw size, county landed, fishing year, month, and area fished (inshore or offshore). The premiums associated with these attributes are highly variable with the largest premiums based on claw size followed by county landed, with south Florida and the Keys having higher price premiums than northwest Florida. There was interannual variation for the month attribute, with the middle of the fishing year having the highest price (January, February) and the lowest was placed on the start and end of each fishing year (October, November, May). These results provide basic economic information and regional insights into one of the most valuable fisheries in Florida and the Gulf of Mexico, and can help inform managers and stakeholders on the balance between profitability and sustainability of this unique fishery.

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.

Incorporating intra-annual variability in fisheries abundance data to better capture population dynamics

To reduce the risk of overexploitation and the ensuing conservation and socio-economic consequences, fisheries management relies on receiving accurate scientific advice from stock assessments. Biomass dynamics models used in stock assessment tend to rely primarily on indices of abundance and commercial landings data. Standard practice for calculating the indices used in these models typically involves taking averages of survey tow data over large, diverse spatial domains. There is a lot of variability in the choice of methodologies used to propagate index uncertainty into the assessment model, many of which require specifying it through expert knowledge or prior distributions. Here we propose an alternative approach that treats each individual survey tow as an independent estimate of the true underlying biomass in the stock assessment model itself. This reduces information loss and propagates uncertainties into the model directly. A simulation study demonstrates that this approach accurately captures underlying population dynamics and reliably estimates variance parameters. We further demonstrate its utility with data from the Inshore Scallop Fishery of south-west Nova Scotia. Results show significant improvements in parameter estimation over previous models while providing similar predictions of biomass with less uncertainty. This reduced uncertainty can improve the resulting scientific advice and lead to improved decision-making by fisheries managers.

Assessing stock status of grey sharpnose shark (Rhizoprionodon oligolinx Springer, 1964) in Java Sea

Increasing demand for shark products leads to over fishing of these species in many areas, damaging their population. Grey sharpnose shark (Rhizoprionodon oligolinx) is caught mostly by gillnet fleet in Java Sea. The objective of the study was to discuss the current stock condition of grey sharpnose shark in Java Sea. Research on shark resources has been conducted by placing enumerators at the main landing base in PPN Pekalongan. Biological parameters of R. oligolinx were estimated based on commercial landings data recorded by enumerators from 2014-2015. The growth parameters of grey sharpnose shark such as L∞, K, t0, values were 96.1 cm, 0.47 year−1, and -0.78 year, respectively. Moreover, total mortality rate (Z) were estimated at 1.82 year−1 with fishing mortality and natural mortality rates (F and M) were 1.04 year−1 and 0.78 year−1, respectively. Stock status of grey sharpnose shark in Java sea from view point of gill nets fisheries is still in the sustainable utilization status with biological reference point more than 30% SPR and level of exploitation rate (E) is 0.57.

Using a state-space population model to detect age-dependent species interactions

Models that incorporate species interactions and their effects on the dynamics of commercially important fish stocks are needed to better understand the importance of ecological interactions and to facilitate sustainable fisheries. We developed a dynamic age-structured population model for the Northeast Arctic stock of Atlantic haddock (Melanogrammus aeglefinus) based on scientific survey and commercial landings data. Our goal was to investigate climate effects and ecological interactions within the haddock food web. A Bayesian state-space framework was used to separate information from ecological noise and observation error. Our results indicate significant impacts of species interactions on haddock dynamics. Haddock survival was associated with biomass indices of cod (Gadus morhua) (negative effect) and capelin (Mallotus villosus) (positive effect). The latter may reflect lower predation by predators such as marine mammals at high capelin biomass. We further detect weak density dependence in the survival of young haddock and a convex relationship between haddock abundance and the scientific survey indices. Our findings highlight the importance of considering natural resources as part of an ecosystem with its diverse interactions both within and between species. This study shows that it is possible to detect ecological interactions with a population model based on noisy data.

Spatio-temporal patterns in demersal elasmobranchs from trawl surveys in the eastern English Channel (1988–2008)

Elasmobranchs have life-history characteristics that make them more vulnerable to fishing than many teleost fish. As commercial landings data are usually not sufficient for the monitoring and assessment of elasmobranchs, fisheries-independent data, geostatistics and Geographic Information Systems were used to investigate the spatio-temporal patterns of sharks (6 species), skates (9 species) and stingray in the eastern English Channel. Temporal trends in relative abundance and distributions of total-length frequencies were investigated using data collected over 21 yr from an annual survey using a Grande Ouverture Verticale (GOV) trawl. Temporal trends in relative abundance were examined qualitatively in relation to the reported conservation status for the various species. Most individuals captured for 7 of the species were immature. The GOV trawl was more efficient at sampling demersal sharks than batoids (skates and rays), especially small-sized batoids. Geostatistics were effectively used to explore, identify and quantify the spatial structure of the distributions of 13 species. The more abundant species displayed significantly larger patch diameters. Three shark species (Scyliorhinus canicula, S. stellaris and Galeorhinus galeus) were found to be spatially segregated by sex. The shark species tended to occur in the deeper waters of the area, while skates were found to be more coastal in their distribution. Results have contributed to a greater understanding of the spatio-temporal patterns in elasmobranch species in the eastern English Channel and are of relevance to future marine spatial planning and the development of long-term management plans for elasmobranchs in the area and elsewhere.

Are the Ugly Truths Not Ugly Enough?

In recent years there has been an increase in the number of papers, many of which have been published in high profile journals, that address real environmental or ecological problems, but with flawed, subjective, and frequently hy- perbolic arguments. I identify two such examples from the US Gulf of Mexico, linked by their focus on fisheries re- sources as the cause de jour, to illustrate the problem and express my concerns. If this trend continues, we should not be surprised when managers and policy makers who need objective, defensible, scientific answers no longer solicit our in- puts. THE UGLY TRUTHS Science, if nothing else, should be objective, and scien- tists who receive funding from public sources are ethically and morally obligated to speak truth to managers and policy makers that work on the public's behalf (1, 2). In recent years, however, there has been an increase in the number of papers, many of which have been published in high profile journals, that address real environmental or ecological prob- lems, but with flawed and subjective arguments. Two such examples are being played out in the Gulf of Mexico, and I use both to illustrate the problem and express my concerns. De Mutsert and coauthors (3) showed that previous analyses using commercial landings data to conclude that marine fish- eries ecosystems in the Gulf of Mexico (GOM) are severely degraded and overexploited (4, 5) were flawed, and overly pessimistic. In their re-analyses, De Mutsert and coauthors (3) used both commercial landings and fishery-independent survey data to show that commercial targeting and high land- ings of target species, and an overly simple definition of a collapse that failed to account for the effects of targeting, variability in fishing effort, and market forces, led to errone- ous conclusions. The aforementioned authors (5) further concluded that all of the worlds capture fisheries would be depleted by the year 2048; this outcome is highly unlikely, and would seem to imply that the fishery management com- munity has learned nothing from past mistakes. There now exist more than 10 published rebuttals of this paper (5) alone. That said, 20% of GOM fisheries have collapsed, but several of these have recovered and others are recovering. Clearly, the most controversial fishery in the GOM is the northern red snapper, which collapsed the late 1980's, when it was commercially extinct in ~50% of its former range. Management of red snapper began in earnest in 1989, and the stock is slowly recovering. More detail is available (3), but user conflict has made management of red snapper espe- cially difficult because recreational and commercial fishers almost equally split the directed harvest, and until recently,

Developing a commercial-vessel-based stock assessment survey methodology for monitoring the U.S. west coast widow rockfish ( Sebastes entomelas) stock

The widow rockfish ( Sebastes entomelas) inhabits the continental shelf and upper slope of the west coast of North America. The U.S. west coast widow rockfish stock has declined since the mid-1980s, leading to implementation of increasingly stringent management restrictions upon the commercial fishery. The low numbers, patchy distribution, and preference for rocky habitats of the widow rockfish make this stock difficult to monitor using standard bottom trawl survey techniques and commercial landings data; currently, there is no reliable index of abundance. An ad hoc government-industry working group began meeting in 2004 to devise a new stock assessment survey strategy. The proposed strategy utilized local fishermen's knowledge of widow rockfish distribution and behavior, chartered commercial fishing vessels, and a combination of fisheries acoustics and underwater video sampling techniques. Results are presented from fieldwork conducted at three study sites off the central coast of Oregon, USA, in March 2005. Acoustic backscatter at 38 kHz between 50 m from the surface to 15 m off the bottom was attributed primarily to widow rockfish. This classification was based on historical widow rockfish distribution at these sites, fish school appearance on acoustic echograms, and deployments of an underwater camera sled. Repeated acoustic sampling along predetermined transects spaced at 0.3 nmi (0.56 km) at two of the study sites documented the temporal and spatial variability of widow rockfish schools over the course of a single day and week-to-week. The CVs of average vertically integrated acoustic backscatter measured in repeated sampling passes at these two sites were 0.31 and 0.36, which are not unreasonable values for a fisheries survey time series. Fine-scale acoustic sampling at a total of three study sites showed that the spatial scale (horizontal dimensions) of the groups of widow rockfish schools observed ranged from 0.2 to 0.8 nmi (0.37–1.48 km). This study demonstrates that sampling of a coastwide suite of study sites selected using local fishermen's knowledge with a standard 38 kHz scientific echosounder, supported by underwater video and limited midwater trawling, may be a promising way of monitoring U.S. west coast widow rockfish abundance. These techniques may also be relevant to monitoring other difficult-to-assess semi-dermersal species inhabiting rocky, untrawlable areas.

Reanalyses of Gulf of Mexico fisheries data: Landings can be misleading in assessments of fisheries and fisheries ecosystems

We used two high profile articles as cases to demonstrate that use of fishery landings data can lead to faulty interpretations about the condition of fishery ecosystems. One case uses the mean trophic level index and its changes, and the other uses estimates of fishery collapses. In earlier analyses by other authors, marine ecosystems in the Gulf of Mexico (GOM) and U.S. Atlantic Ocean south of Chesapeake Bay were deemed to be severely overfished and the food webs badly deteriorated using these criteria. In our reanalyses, the low mean trophic level index for the GOM actually resulted from large catches of two groups of low trophic level species, menhaden and shrimp, and the mean trophic level was slowly increasing rather than decreasing. Commercial targeting and high landings of shrimps and menhaden, especially in the GOM, drove the index as previously calculated. Reanalyses of fishery collapses incorporating criteria that included targeting, variability in fishing effort, and market forces discovered many false cases of collapse based simply upon a decline of catches to 10% of previous maximum levels. Consequently, we suggest that the low mean trophic level index calculated in the earlier article for the GOM did not reflect the overall condition of the fishery ecosystem, and that the 10% rule for collapse should not be interpreted out of context in the GOM or elsewhere. In both cases, problems lay in the assumption that commercial landings data alone adequately reflect the fish populations and communities.

Using commercial landings data to identify environmental correlates with distributions of fish stocks

AbstractWe examined the efficacy of using commercial landings data to identify potential environmental correlates with fish distributions. Historical landings data for two commercially important species, Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus), were used along with historical conductivity, temperature, and depth (CTD) data to infer monthly mean spatial distributions of catch per unit effort (CPUE), temperature, salinity, density, and stratification over Georges Bank. Relationships between CPUE and these environmental variables plus bottom sediment type and bottom depth were examined on seasonal, annual, and interannual time scales. Empirical analysis suggests that both cod and haddock are found preferentially in water temperatures of approximately 5°C in winter/spring, and as high as 10–11°C during late fall. Both species are also found preferentially over coarse sand and gravel as opposed to fine sand, and in water depths between 60 and 70 m. These preferences appear to vary seasonally. The above results are consistent with findings of previous investigators using semi‐annual research trawl survey data, and suggest that commercial landings data, despite their known errors and biases, can be used effectively to infer associations between fish and their environment.

Distribution patterns of key fish species of the southern Benguela ecosystem: an approach combining fishery-dependent and fishery-independent data

Within the context of an ecosystem approach for fisheries, there is a need for quantitative information on distributions of key marine species. This information is valuable input for modelling species interactions in the southern Benguela ecosystem. In the present study, a method is described for mapping the density distribution of 15 key species: anchovy Engraulis encrasicolus, sardine Sardinops sagax, round herring Etrumeus whiteheadi, chub mackerel Scomber japonicus, horse mackerel Trachurus trachurus capensis, lanternfish Lampanyctodes hectoris, lightfish Maurolicus muelleri, albacore Thunnus alalunga, bigeye tuna Thunnus obesus, yellowfin tuna Thunnus albacares, silver kob Argyrosomus inodorus, snoek Thyrsites atun, Cape hake Merluccius spp., kingklip Genypterus capensis and chokka squid Loligo vulgaris reynaudi. The purpose was to make use of all available sources of data to extend the spatial and temporal coverage of the southern Benguela. Six sources of data were combined on a 10′ × 10′ cell grid in a Geographical Information System: acoustic and demersal surveys conducted by Marine and Coastal Management (MCM), and pelagic, demersal (including midwater trawl), hake-directed and tuna-directed longline commercial landings data collected by MCM. Comparisons of distributions between two periods (1980s and 1990s) and between two semesters (April – September and October – March) were conducted, but biases as a result of major differences in sampling strategy prevented detailed analysis for certain species. Maps of density distributions are nevertheless presented here and the method to determine them is discussed.

Objective methods for defining mixed-species trawl fisheries in Spanish waters of the Gulf of Cádiz

This paper presents the results obtained from applying an objective classification method to the daily commercial landings data of the Spanish bottom-trawl fishery off the Gulf of Cádiz for defining mixed-species fisheries or fishing trip types. Definition of these operational fisheries was based on the relatively unique and homogeneous species composition of the landings and technical characteristics of the vessels. The method was based on cluster (CA) and linear discriminant (DA) analysis techniques. The application of CA techniques to the 1993 data matrix of daily catch per unit of effort per species and active vessel resulted in the identification of 22 types of fishing trips, which were defined by the relative importance of their target and accessory species. Subsequently, different linear discriminant functions were derived for each FTT in order to classify new records. Five different fleet types were also identified through CA techniques according to the vessel’s length, GTR and HP. The distribution of active vessels by fleet type in each landing port showed a great local and regional heterogeneity of the fleets exploiting the multispecies fishery. A correspondance analysis between types of fleets and fishing trips showed a high correlation, indicating the existence of a direct relationship between the capacity of vessel mobility and the bathymetric situation of the fisheries.

Aspects of the stock dynamics and exploitation of cuttlefish, Sepia officinalis (Linnaeus, 1758), in the English Channel

Basic biological parameters of cuttlefish, Sepia officinalis, in the English Channel are described from samples of commercial and research vessel landings made between April 1994 and September 1995. There was a significant difference between the length–weight relationship of male and female cuttlefish. Growth of both sexes was rapid and seasonal during the last 12 months of life. Males grew faster than females, and reached larger overall lengths and weights. Most males reached maturity before the start of their second winter, although the testis continued to develop until spawning took place the following spring. Female maturation began later and was more prolonged such that it was completed towards the end of the second winter. Adults of both sexes spawned after the second winter between late March and July. Commercial landings data showed spawning cuttlefish initially arrived on inshore grounds in the western Channel, but slightly later and in greater numbers on the inshore grounds of the middle and eastern Channel. The weight and value of cuttlefish landings made by UK vessels in the Channel increased greatly between the mid 1980s and the mid 1990s such that cuttlefish are now a major part of the earnings for several fisheries. The most important fisheries were the offshore beam trawls, and inshore otter trawls and nets. The exploitation pattern of each fishery is described from quarterly samples of commercial landings taken between April 1994 and March 1996. Each exploitation pattern is shown to be a function of the region fished, the catching gear employed, and the growth and migrations of the cuttlefish population. Some implications for stock management are discussed.

Estimation of Unreported Catch in a Commercial Trawl Fishery

This paper describes a systematic approach that combines research survey and commercial landings data to estimate the total catch of a species, including discards, in a commercial trawl fishery. The method is applied to the 1989 Norwegian bottom trawl fishery for cod (Gadus morhua L.) in the Barents Sea and its utility is evaluated. Bottom trawl survey data together with results from cod-end selectivity studies of the regulated mesh size are used to determine the 'expected' commercial catch composition in percent-at-length, thereby simulating the catch composition of a commercial vessel fishing at randomly located stations. The commercially landed fish numbers-at-length are adjusted upwards to reflect these ‘expected' catch levels. The minimum legal market length is then used for a knife-edge estimate of numbers likely to have been discarded. Results indicate a 7.4% increase in the 'estimated' total catch in 1989 over the numbers landed. Of this increase, 732 000 fish or 6.9% of the total catch would have been discarded or not reported as catch. Results are plausible as examined through comparison of 'estimated' catch mean lengths with mean lengths from: 1) the 1989 Norwegian commercial catch of cod sampled through a surveillance program; 2) 1989 standard Norwegian trawl surveys; and 3) a 1989 cooperative trawl survey in the Barents Sea. Comparisons illustrate basic differences in length selection between survey and commercial trawl gear, and effective differences in mean lengths of catches from randomized surveys and commercially directed fisheries.

Fish impingement at estuarine power stations and its significance to commercial fishing

The abstraction of cooling water at power stations sited on tidal waters inevitably leads to mortalities of some fish which are drawn in with the cooling water supply and become impinged on the intake screens. These fish are predominantly 0‐ or I‐group juveniles which, owing to their small size, are unable to resist intake currents.Commercial fishermen often object to the fact that juvenile fish are killed in this way. Their concern stems from the fact that, in order to protect stocks, commercial fishing is restricted to fish which are above a statutory minimum landing size, whereas the majority of fish killed by impingement are below this size.This paper considers the significance of impingement mortalities at estuarine sites in Britain for six commercially important species: cod, Gadus morhua, whiting, Merlangius merlangus, plaice, Pleuronectes platessa, dab, Limanda limanda, sole, Solea solea and herring, Clupea harengus. Life tables are used to establish expected survival trajectories for each species and to compute reproductive potential. Each fish killed on intake screens is then considered in terms of the fraction of the reproductive potential of a single adult at maturity, and is ascribed an ‘adult equivalent’ value. Total catches of mixed juveniles and adults are then presented as ‘adult equivalent’ values. The results are then compared with commercial landings data and it is shown that catches by power stations are trivial in comparison with commercial landings.

Population age structure and mortality rates of jackass morwong ( Nemadactylus macropterus) in Eastern Bass Strait, Australia

The catch-curve method was used to estimate the instantaneous rate of total mortality ( Z) of jackass morwong ( Nemadactylus macropterus) in south-east Australian waters. Age-frequency distributions were obtained for fish collected from eastern Bass Strait during the 3 years. March 1982–February 1985. Fish were obtained from: (1) demersal research fishing surveys stratified by depth; (2) commercial landings from eastern Bass Strait; (3) commercial landings from the adjacent New South Wales fishery. Jackass morwong were found in water 65–299-m deep, and almost half the biomass was in water 90–179-m deep. Our estimate of the total biomass (from the survey results) of the part of the population in eastern Bass Strait was 15 700 t. The oldest male morwong caught was 11 years old, the oldest female 13 years old. From the survey data, total mortality ( Z) was estimated as 0.45 for males, which is equivalent to an annual survival rate ( S) of 0.64, and as 0.47 for females, equivalent to an S of 0.63. There was substantial annual variation in estimates of Z. For the survey results, the annual mortality rate estimated for males was significantly different from that for females. The instantaneous rate of fishing mortality ( F) estimated from population biomass and mean commercial landings was very low (about 0.024; sensitivity analysis indicated a possible range of 0.012–0.072), and indicated that about 2% (by number; range 1–6%) of the part of the population in eastern Bass Strait was harvested annually. Z values estimated from samples of commercial landings were consistently larger than Z estimated from the survey samples. Using estimates of Z from commercial landings data resulted in high values of M (the instantaneous rate of natural mortality), which were inconsistent with the longevity of the species and the proportion of older fish found in the population. We believe this to be due to bias in the way commercial landings sample the population, and to be an inherent bias in the use of age-frequency data from commercial landings unless some correction for size-selectivity due to commercial fishing gear and fishing behaviour can be made.