Cod Catch Research Articles

Condition, size, and winter duration affect winter survival probability of juvenile Atlantic cod Gadus morhua in a coastal subarctic ecosystem

Juvenile Atlantic cod Gadus morhua in coastal Newfoundland, Canada, settle in nearshore habitats in 3-6 pulsed events each year, from mid-summer to early winter, creating a broad size range of age-0 fish within each year-class, with potentially different survival trajectories entering their first winter. We hypothesized that early-arriving pulses, high autumn body condition, and low winter severity would contribute to high first-winter survival of age-0 cod. To test these hypotheses, we examined juvenile cod catch data, archived samples, and winter temperature records to determine the impact of winter duration, body condition, and settlement time on winter survival from 2001 to 2019. Settlement pulse, pre-winter condition, and winter duration had an interactive effect on survival. Fish condition did not vary across pulses within a given year-class, but we observed improved winter survival during long winters when body condition was high, with highest survival among the larger, early-arriving pulses of fish. Late-arriving pulses of fish were small-sized before winter onset, but these pulses unexpectedly survived better than pulses settling earlier in the season during short winters when body condition was high. However, all settlement pulses had a survival advantage when settlement occurred earlier on average (associated with warmer autumns), suggesting that increased growth and size within a pulse can also contribute to overwintering success. Our findings challenge some assumptions of overwintering ecology (e.g. ‘bigger is better’, low temperature stress) but illustrate the importance of cohort effects for overwintering survival in a sub-arctic marine ecosystem in a changing climate.

The effects of LED handline attachments on Atlantic cod (Gadus morhua) catch efficacy and bycatch

Catch efficacy and bycatch are critical factors that determine the sustainability, practicality, and profitability of fishing gears. Inshore Atlantic cod (Gadus morhua) fisheries commonly use gillnets, cod-pots, longlines and handlines. Owing to their efficiency, selectiveness, and low effort, gillnets are the most widely used gear. Gillnets however are prone to bycatch and low-quality catch. Handlines benefit from low capital investment, live high-quality fish, low bycatch, and low carbon footprint. Enhancements to handlines that could increase catch rate or size of catch would be considered beneficial and could promote uptake by harvesters using other gear types. Previous pilot research has shown that LED handline attachments that target the visual sensitivity of cod increased the catch rate of Atlantic cod. The present study builds upon this finding, incorporating three participating commercial crews and vessels. We found no significant effect of LED handline modifications on catch efficacy for Atlantic cod or bycatch. The bycatch of Atlantic wolffish (Anarhichas lupus) in our study was found to decrease with the use of green LEDs, but the data precludes complex statistical analysis. We discuss how these findings are relevant to small-scale fishers and provide an empirical reference regarding the use of such devices in the commercial fishery.

An evolution of pontoon traps for cod fishing (Gadus morhua) in the southern Baltic Sea

With increasing seal populations in the Baltic Sea comes growing interaction between seals and coastal fisheries. The impact of seals, mainly grey seal (Halichoerus grypus), on fisheries can be reduced by implementing of seal-safe fishing gear, which hinders seal access to catches. One successful solution is the introduction of a modified seal-safe trap net, the pontoon trap. In this study, pontoon traps were modified for use in cod (Gadus morhua) fisheries in the southern Baltic Sea. Three aspects of the pontoon trap design were tested for their effects on catch rates: (1) leader net mesh size; (2) leader net length; and (3) fish chamber position. The greatest catch rates were obtained using a leader net with a 100 mm center-knot to center-knot mesh-size on a bottom-set fish chamber while there was no difference in cod catch rates in relation to leader net length. There was no seal-induced damaged cod in the pontoon traps during any of the trials. Cod catch rates using the pontoon trap were also compared to those of the cod gillnet fishery in the same area. The comparison showed that during specific fishing occasions, multiple pontoon traps may have similar catch rates to gillnets.

The North Atlantic Fish Revolution (ca. AD 1500)

AbstractWe propose the concept of the “Fish Revolution” to demarcate the dramatic increase in North Atlantic fisheries after AD 1500, which led to a 15-fold increase of cod (Gadus morhua) catch volumes and likely a tripling of fish protein to the European market. We consider three key questions: (1) What were the environmental parameters of the Fish Revolution? (2) What were the globalising effects of the Fish Revolution? (3) What were the consequences of the Fish Revolution for fishing communities? While these questions would have been considered unknowable a decade or two ago, methodological developments in marine environmental history and historical ecology have moved information about both supply and demand into the realm of the discernible. Although much research remains to be done, we conclude that this was a major event in the history of resource extraction from the sea, mediated by forces of climate change and globalisation, and is likely to provide a fruitful agenda for future multidisciplinary research.

More data for the money: Improvements in design and cost efficiency of electronic monitoring in the Danish cod catch quota management trial

Electronic Monitoring (EM) with video is a tool often mentioned to ensure compliance with fishing regulations while vessels are at sea. Since 2008, several trials have been conducted in the European Union on the use of EM. One of the largest and longest running European trials was the 2010–2016 Cod Catch Quota Management trial (CCQM) in Denmark. This paper reviews the methods and experiences gained from this trial, with focus on the last two years where criteria for video audits were expanded and major technical developments took place. The cost-effectiveness and potential of EM for compliance, management and scientific purposes is discussed. The present study demonstrates that EM is capable of high precision detection of non-compliance with a discard ban and that developments in the transmission of EM data allowed for a smoother and more reliable Monitoring, Control and Surveillance (MCS) system. Although further developments are needed, especially within the field of automated image analysis, we conclude that EM is one of the few feasible tools where fisheries information and compliance can be ensured under a Landing Obligation.

Assessing a Threatened Fish Species under Budgetary Constraints: Evaluating the Use of Existing Monitoring Data

AbstractBecause of the high costs of collecting field data, many species recovery and management plans do not include a monitoring feedback component to measure the success of interventions and refine management strategies. Here, we demonstrate how leveraging existing monitoring data can provide broad‐scale, cost‐effective information about a threatened fish species, the Murray Cod Maccullochella peelii, which is of cultural and recreational importance in Australia. We applied a Bayesian hierarchical model of abundance to Murray Cod catch data collected as part of broad‐scale, general condition monitoring in the Murray–Darling Basin. The model uses replicated sampling at spatially independent sites to disentangle the confounding effects of detection probability and abundance on catch data. We demonstrate the reliability of the analysis for determining trends in abundance with a simulation study, and we show that basinwide abundance of Murray Cod declined by over 50% between 2010 and 2013. We found that detection probability of Murray Cod can vary substantially across space and through time, suggesting that accounting for variable detection will be important in any future evaluation of Murray Cod populations. This study highlights variable detection as an issue in monitoring regimes and demonstrates a method for the cost‐effective use of existing monitoring data to evaluate species abundance trends.

New England Cod Collapse and the Climate.

To improve fishery management, there is an increasing need to understand the long-term consequences of natural and anthropogenic climate variability for ecological systems. New England’s iconic cod populations have been in decline for several decades and have recently reached unprecedented lows. We find that 17% of the overall decline in Gulf of Maine cod biomass since 1980 can be attributed to positive phases of the North Atlantic Oscillation (NAO). This is a consequence of three results: i) a 1-unit increase in the NAO winter index is associated with a 17% decrease in the spring biomass of age-1 cod the following year; ii) this NAO-driven decrease persists as the affected cohort matures; iii) fishing practices appear to exacerbate NAO’s direct biological effect such that, since 1913, a 1-unit increase in the NAO index lowers subsequent cod catch for up to 19 years. The Georges Bank cod stock displays similar patterns. Because we statistically detect a delay between the NAO and subsequent declines in adult biomass, our findings imply that observed current NAO conditions can be used in stock forecasts, providing lead time for adaptive policy. More broadly, our approach can inform forecasting efforts for other fish populations strongly affected by natural and anthropogenic climatic variation.

Spatial partitioning in the use of structural woody habitat supports the cohabitation of two cod species in a large lowland river

Many freshwater fish worldwide have been shown to use Structural Woody Habitat (SWH) for a variety of reasons. The mid reaches of the Murray River, a large lowland river in south-eastern Australia, was surveyed by boat electrofishing, to investigate the use of SWH type (hollows, rootmass and solids), SWH distance to bank (near bank, intermediate to bank and mid-channel) and the interaction between SWH type and distance to bank. The study found that Murray cod catch per unit effort (CPUE) increased in near-bank areas when hollows were a component of the SWH. The CPUE of trout cod was higher when hollows were present. However, the interactions between distance to bank and hollow SWH were complex and dependent on presence or absence of rootmass. The species-specific interactions between SWH microhabitat and distance to bank found within this study has important relevance for stream managers. The common practice of realigning SWH favours Murray cod over trout cod, which could have negative consequences for the endangered trout cod. More broadly, managers may need to consider a balance of SWH type and where it is placed in the river for the species they are targeting when rehabilitating rivers via the introduction of SWH.

Historical Arctic Logbooks Provide Insights into Past Diets and Climatic Responses of Cod.

Gadus morhua (Atlantic cod) stocks in the Barents Sea are currently at levels not seen since the 1950s. Causes for the population increase last century, and understanding of whether such large numbers will be maintained in the future, are unclear. To explore this, we digitised and interrogated historical cod catch and diet datasets from the Barents Sea. Seventeen years of catch data and 12 years of prey data spanning 1930–1959 cover unexplored spatial and temporal ranges, and importantly capture the end of a previous warm period, when temperatures were similar to those currently being experienced. This study aimed to evaluate cod catch per unit effort and prey frequency in relation to spatial, temporal and environmental variables. There was substantial spatio-temporal heterogeneity in catches through the time series. The highest catches were generally in the 1930s and 1940s, although at some localities more cod were recorded late in the 1950s. Generalized Additive Models showed that environmental, spatial and temporal variables are all valuable descriptors of cod catches, with the highest occurring from 15–45°E longitude and 73–77°N latitude, at bottom temperatures between 2 and 4°C and at depths between 150 and 250 m. Cod diets were highly variable during the study period, with frequent changes in the relative frequencies of different prey species, particularly Mallotus villosus (capelin). Environmental variables were particularly good at describing the importance of capelin and Clupea harengus (herring) in the diet. These new analyses support existing knowledge about how the ecology of the region is controlled by climatic variability. When viewed in combination with more recent data, these historical relationships will be valuable in forecasting the future of Barents Sea fisheries, and in understanding how environments and ecosystems may respond.

Recreational Fishing Effort, Catch, and Harvest for Murray Cod and Golden Perch in the Murrumbidgee River, Australia

AbstractRecreational fishery management aims to prevent species decline and provide sustainable fisheries. Overfishing has been frequently suggested as a cause of historic fishery declines within the Murray–Darling Basin (MDB), Australia, but there have been few quantitative surveys for providing fishery‐dependent data to gauge status. The Murray Cod Maccullochella peelii and the Golden Perch Macquaria ambigua are important species targeted by recreational fishers across the MDB. The fisheries are controlled by size and bag limits and gear restrictions (both species) as well as a closed season (Murray Cod only). A complemented fisher survey design was used to assess the recreational fishery for both species in a 76‐km reach of the Murrumbidgee River in 2012–2013. Progressive counts were used to quantify boat‐ and shore‐based fishing effort. Catch and harvest rate information was obtained from shore‐based fishers via roving surveys and from boat‐based fishers via bus route surveys. Murray Cod catch rates (fish/angler‐hour) were 0.228 ± 0.047 (mean ± SE; boat based) and 0.092 ± 0.023 (shore based), and harvest rates (fish/angler‐hour) were 0.013 ± 0.006 (boat based) and 0.003 ± 0.001 (shore based). Golden Perch catch rates were 0.018 ± 0.009 (shore based) and 0.002 ± 0.001 (boat based), and harvest rates were 0.006 ± 0.002 (shore based) and 0.001 ± <0.001 (boat based). The Murray Cod fishery had maximal catch and harvest during the 5‐month period after the closed season ended. The closed season aims to protect spawning Murray Cod, but this strategy's effectiveness may have been influenced by high fishing effort and deliberate bycatch during the closure period. To sustain and improve these MDB fisheries, we suggest quantification of catch‐and‐release impacts on spawning Murray Cod, provision of fish passage, re‐stocking of Golden Perch, and education on fishing techniques that minimize Murray Cod bycatch during the closed season.Received October 22, 2014; accepted March 6, 2015

Too Hot to Handle: Federal Public Trust Doctrine as Basis for United States Responsibility for Global Warming-Induced Migration of New England Cod

Does the United States federal government have a fiduciary responsibility to protect the federally governed oceans and their resources for the citizens of the United States? Is this responsibility housed in a public trust theory where the government is the fiduciary trustee and the citizens are the trust beneficiaries? If not, where does the responsibility lie?Global warming has raised ocean temperatures such that Northwest Atlantic cod stocks are moving northward and deeper to reach cooler waters. This change is now a factor in the severely reduced groundfish populations in the United States’ New England Atlantic region. Deemed officially overfished with active overfishing, the New England Fishery Management Council recently voted to reduce cod catch rates by seventy-seven percent in the Gulf of Maine and by sixty-one percent in the Georges Bank area near Cape Cod, to become effective May 1, 2013. This paper argues, like others that have come before it, that long-overdue acceptance of a federal public trust doctrine recognizes a fiduciary responsibility in the federal government for protection of public trust assets, specifically the marine environment and its resources. However, it goes further to assert that this duty can provide the legal basis for a breach of trust claim against the federal government for failure to prevent and mitigate damages to marine resources from the ocean warming effects of greenhouse gas emissions. While the intent is to expedite and strengthen legislative and regulatory preventative action addressing the problem source, a recognized federal responsibility also provides a strong foundation for Congressional budgetary appropriations for remedies to the damaged fishers of the United States’ New England Atlantic region. This paper further suggests that a stronger, more decisive federal response to greenhouse gas emissions will instigate, in interplay with market principles, innovative formation of a permanent solution to the devastating impact of greenhouse gas emissions on our oceans and the living resources in them.

Ecological relationship between environmental factors and Pacific cod (Gadus macrocephalus) catch in the southern East/Japan Sea

The habitat characteristics of Pacific cod (Gadus macrocephalus) and the ecological relationship between Pacific cod catch and environmental parameters in the southern East/Japan Sea were investigated. Pacific cod is sexually matured at age of 4–5. The highest catch of Pacific cod off the eastern Korean Peninsula occurred in seawater temperature range of 0–4°C and salinity range of 33.8–34.2 practical salinity unit at 100 m. The Cross-Correlation Function analysis showed that there was a significant negative correlation between Pacific cod catch and February seawater temperature at 75 m nearby spawning area with a time lag of 5 years in Korean waters (r = –0.360, p < 0.05). The annual catch of Pacific cod also had a significant correlation (p < 0.05) with zooplankton biomass in coastal nursery areas with a time lag, i.e., the highest ones, r = 0.432 and r = 0.452, for total zooplankton biomass in June of 5 years ago, and for euphausiids abundance in February of 4 years ago from the period when Pacific cod was caught, respectively. Furthermore, total catches of Pacific cod in the southern East/Japan Sea (i.e., sum of Korean and Japanese catches) were negatively correlated with winter Arctic Oscillation Index, and the highest negative correlation (r = –0.364, p < 0.05) was shown with a time lag of 4 years. Considering sexual maturation at ages 4–5, such statistical analyses imply that biotic and abiotic environmental factors during the early life stages of Pacific cod have a significant influence on recruitment after 4–5 years of spawning.

Mixed fisheries management: protecting the weakest link

North Sea cod Gadus morhua stock is outside safe biological limits, and total allowable catch (TAC) management has proved ineffective to rebuild the stock. The European Commission is considering the imposition of a discard ban to preserve vulnerable and economically important fish stocks. We explored the potential effects of a discard ban in mixed fisheries management using the French mixed fisheries in the Eastern English Channel as a model system. We examined in particular the performance of 2 different management scenarios: (1) individual quota management with a tolerance for discarding and (2) individual quota management in combination with a discard ban, using a dynamic state variable model. The model evaluates a time series of decisions taken by fishers to maximize profits within management constraints. Compliance to management was tested by applying an in-height varying fine for exceeding the quota. We then evaluated the consequences of individual cod quota in both scenarios with respect to over-quota discarding, spatial and temporal effort allocation and switching between metiers. Individual quota management without a discard ban hardly influenced fishers' behaviour as they could fully utilise cod quota and continue fishing other species while discarding cod. In contrast, a discard ban forced fishers to reallocate effort to areas and weeks in which cod catch is low, at the expense of lower revenue. In general, a restrictive policy for individual quota for cod needs to be combined with a discard ban and a high fine ( 20 times the sale price) to reduce over-quota discarding.

Learning How to Fish: Catch Shares and the Future of Fishery Conservation

I. INTRODUCTION II. THE TRAGEDY OF THE OCEAN COMMONS III. THE FAILURE OF FISHERY REGULATION IV. PROPERTY RIGHTS--THE ROAD NOT TAKEN V. CATCH SHARES IN PRACTICE A. Economic Consequences of Catch Shares B. Catch Shares and Conservation C. Social and Economic Consequences of Catch Shares VI. THE IMPORTANCE OF PROPERTY RIGHTS VII. CONCLUSION I. Introduction In a crowded meeting hall in Portsmouth, New Hampshire, the New England Fishery Management Council voted this January to recommend drastic new cuts to the catch limits for Atlantic codfish off the New England coast. (1) Over the strenuous objections of local communities and fishermen, the Council proposed 77% reductions in the allowable cod harvest for each of the next three years in the Gulf of Maine, and a 61% cut in next year's cod catch on Georges Bank. (2) The National Oceanographic and Atmospheric Administration approved the proposed catch limits and other emergency measures in May 2013. (3) New England fishermen and other opponents of the plan fear that these restrictions will doom the centuries-old local fishing industry. As one lamented- Right now what we've got is a plan that guarantees the fishermen's extinction and does nothing to ameliorate it. (4) Proponents of the plan, however, counter that these measures are the only way to save the rapidly collapsing Atlantic cod industry. As Council member John Bullard, regional administrator of the National Oceanic and Atmospheric Administration, observed, the problem is that there are fewer and fewer codfish in the sea. It's midnight and getting darker when it comes to how many cod there are. There isn't enough cod for people to make a decent living. (5) The dire state of the fishery gave Council members little choice. (6) Unfortunately, even these severe new limits may not be enough to save the New England cod fishery. The Council's most recent steps follow on years of mismanagement, overly optimistic stock estimates, and misguided fishery policies that failed to align the economic interests of the fishing community with the long-term sustainability of the fishery. Reforms adopted for the 2010 season may have been too little too late. (7) As fishery researcher Ray Hilborn has explained, the incentives and policies governing the New England groundfish fishery for many years have made the fishery vulnerable to just this kind of collapse. (8) In the 1990s, for example, the fishery stock assessments indicated that short-term catch limits and fishing effort reductions could rebuild the fishery stock and ultimately lead to higher long-term yields. Nevertheless, local fishermen and their political representatives vehemently opposed any such reductions. (9) It would be easy to attack New England fishermen for being short-sighted. To do so, however, would ignore the incentives they face--incentives created by the existing regulatory structure. Due to a large number of inactive trawling permits, incumbent fishermen have little incentive to agree to catch reductions, as they would be unlikely to capture the full value of the rebuilt stocks. (10) Even if catch reductions today would lead to higher catch limits in the future, a rebuilt stock could encourage inactive trawlers to resume fishing. (11) And although a variety of forces--some beyond human control--likely contributed to the fishery's present crisis, without proper incentives for the fishing community to preserve New England's stocks, overfishing and mismanagement continued, leaving one of North America's oldest fisheries increasingly vulnerable to collapse. The hard choices being made in an effort to save the Atlantic cod fishery today are all too common, as policymakers continue to employ and rely upon failed conservation policies, leaving fisheries the world over poorly managed and under stress. (12) By some measures, a majority of exploited fisheries are depleted or in decline. (13) Even more troubling, new research suggests that those fisheries about which scientists know the least may be in the worst shape. …

Development of new concepts for escape windows to minimise cod catches in Norway lobster fisheries

Gear selectivity with regard to cod ( Gadus morhua) needs to be improved in the Kattegat and Skagerrak Norway lobster ( Nephrops norvegicus) fishery. One way to achieve this goal is to improve the selectivity of an escape window (henceforth window) in the gear. Our gear development focused particularly on moving the window further back, gaining more stability in the codend to avoid loss of Norway lobster through the window, making a relatively narrow section where the window is located, and testing larger mesh sizes in the window. We designed a four-panel sorting section—the sorting box—where a 300 mm window is placed at the top section at about 3–6 m from the codline. Acoustic release technology was used to avoid catch loss during gear retrieval. Sea trials were conducted in the Skagerrak and Kattegat from a commercial trawler. The sorting box yielded a high reduction of the cod catch, but no improvement was observed for cod that came into contact with the window after reducing the distance from the window to the codline. The sorting box also showed a high reduction of flatfish and other roundfish species. The retention of Norway lobster above minimum landing size in the sorting box was higher compared to a general selection model.

Gulf of Maine cod in 1861: historical analysis of fishery logbooks, with ecosystem implications

AbstractSince 2000, virtually every major assessment of ocean policy has called for implementing an ecosystem approach to managing marine resources, yet crafting such an approach has proved difficult. Ecosystems today exhibit little of the abundance and complexity found in the past, and populations of over‐fished species have declined dramatically world‐wide, yet historical evidence has been difficult to assimilate into complex ecosystem models. Here, we look to the testimony of Gulf of Maine fishermen for insights on the abundance of Atlantic cod (Gadus morhua) and the environment that once supported such large numbers of them. Using logbook data from Frenchman’s Bay, Maine, and other New England communities at the time of the Civil War, we estimate cod landings in the Gulf of Maine in 1861, establish a population structure for cod at that time, and map the geographical distribution of fishing effort of a fleet that minimized risk and cut expenses by fishing inshore where cod and bait species were plentiful. Log entries list the pelagic and bottom‐dwelling invertebrate species these fishermen used for bait, when and how they acquired it, and what species they looked for in the water to signify the presence of cod. Ranked descriptions of both cod and bait abundance were found to be statistically significant indicators of cod catch. Frenchman’s Bay fishermen 140 years ago provided a minimum set of ecosystem requirements for abundant cod, conditions that may inform management plans aimed at restoring both the species and the Gulf of Maine marine ecosystem.

Atlantic cod (Gadus morhua) distribution response to environmental variability in the northern Gulf of St. Lawrence

Atlantic cod ( Gadus morhua ) distribution patterns and the behavioral (site fidelity), biotic (prey and predators), and environmental factors that determine them are fundamental to cod’s historic importance as a commercial species in the North Atlantic. Using classification and regression tree analysis (CART), we compared two periods (1991–1995 and 1998–2004) with contrasting bottom temperature and salinity regimes to determine regional factors that best explained cod distribution and catch weight per tow from summer surveys in the northern Gulf of St. Lawrence (the feeding period of cod). The classification tree analysis indicated that the presence or absence of cod was chiefly determined by depth in both of these periods. In contrast, the regression tree analysis determined that cod catch weight distributions were explained by different variables in each period. In the colder period (1991–1995), the distribution of catch weights was explained well by environmental variables (bottom temperature, salinity, depth); however, in the warmer period (1998–2004), distributions were best explained by variables from the previous year. These results indicate that the spatiotemporal dynamics of environmental conditions are likely to influence the loyalty of cod to specific feeding grounds and imply that cod responses to the environment could be susceptible to long-term environmental (e.g., bottom–habitat) and climate change.

Cod bycatch in otter trawls and in longlines with different bait types in the Georges Bank haddock fishery

In the Northwest Atlantic, bycatch of depleted groundfish stocks in the haddock fishery on Georges Bank is an ongoing concern. In recent years, this fishery on the American side of Georges Bank has been limited by high bycatch rates of cod. Considerable conservation engineering work has been done to address the problem, including experiments with different longline baits and modifications to otter trawl gear. Fabricated baits have shown promise for increased selectivity when longlining, but it has sometimes been difficult to establish whether low cod catch rates with fabricated baits have resulted from bait selectivity or from a low abundance of cod in the area. In this study, we compare catch rates of cod and haddock between otter trawls and longline gear in experimental and commercial fishing on Georges Bank in the summer of 2005. We also compare cod bycatch rates among longlines baited with squid, herring, or fabricated baits (mainly Norbait 700E) in Georges Bank Closed Area 1, from October 2003 to June 2005. Records from the Northeast Fisheries Observer Program were combined with data collected by the Cape Cod Commercial Hook Fishermen's Association (CCCHFA), and compared using generalized linear models. In the Eastern US-Canada Resource Sharing Area (EUSCA) in the summer of 2005 catch of cod per haddock by weight was significantly lower when fishing with longline gear (0.008–0.045 kg cod per kg haddock) than with otter trawl gear (0.059–0.826 kg cod per kg haddock), in all months and areas. Cod bycatch rates were also significantly lower for longlines fishing for haddock than for otter trawls fishing for groundfish species other than haddock. In Closed Area 1, statistically significant differences in cod to haddock ratios were found between baits, with squid catching the highest amount of cod, fabricated baits catching the lowest amount, and herring at an intermediate level. The development of fishing methods that minimize cod bycatch is a high priority in many regions of the North Atlantic. These results indicate that longlines with fabricated bait have the potential to maintain a very low catch of cod while fishing for haddock.

Analysis of cod catch data from Icelandic groundfish surveys using generalized linear models

Abstract Catch data from the Icelandic groundfish surveys are analyzed using generalized linear models (GLM). The main goal is to test the effects of environmental variables on the expected cod catch and to distinguish between the gamma and log-normal distributions for the error structure. Only positive catch data are included in this work, i.e. only the positive part of a delta–gamma or delta–log-normal distribution is examined. The distributions are compared via a Kolmogorov–Smirnov goodness of fit test. Polynomials are used to describe the relationship between each environmental variable and the cod catch and their effects are tested within the GLM framework (a continuous model). Finally, an attempt is made to locate temperature fronts in the ocean by estimating the temperature gradient vector at each data point. The effect of the size of this gradient vector is then tested within in the GLM framework. A stratification model with only spatial and time effects explains 80% of the variation but that comes with a high cost of degrees of freedom. Most of the tested effects are found to be significant but the continuous model only captures 45% of the total variation. The size of the temperature gradient vector is found to be statistically significant though only a small portion of the variation in the data is explained by this term.

Reconciling overfishing and climate change with stock dynamics of Atlantic cod (Gadus morhua) over 500 years

To examine overfishing and climate effects on depleted cod (Gadus morhua) stocks, a surplus production model based on reconstructions of cod catch in Newfoundland was used to describe biomass dynamics from 1505 to 2004. Productivity parameters r (population growth rate) and K (carrying capacity) were assigned by fitting model to survey biomass. Assumptions of fishery-only influences inferring constant, random, or depensatory parameters fared poorly (did not mimic history), as did climate influences indexed by tree ring growth. However, a model using both climate and depensation fared well, mimicking much documented history of Newfoundland cod, including declines during the Little Ice Age (mid- to late 19th century) and the stock collapses of the late 20th century, with a good fit to recent scientific surveys (r2 = 0.80). This model suggests temporal differentiation between fishing and climate effects, including (i) declines during the Little Ice Age (1800–1880) caused by lower productivity, (ii) collapses in the 1960s caused by overfishing, (iii) collapses in the late 1980s caused by both, and (iv) rebuilding now hindered by depensatory effects of low numbers.