NAFO Subarea Research Articles

Using genomic tools to inform management of the Atlantic northern fulmar

Highly migratory species pose unique conservation and management challenges, especially when significant mortality occurs away from breeding concentrations. Population genetics and genomics may help with the appropriate management of these species by (1) determining the population genetic structure of a species across its range, and (2) allowing the assignment of individuals to their breeding source. The northern fulmar (Fulmarus glacialis; Procellariiformes: Procellariidae) is a seabird species that breeds in colonies throughout the North Atlantic and Pacific oceans. This species ranges widely across ocean basins during the non-breeding season and is exposed to a variety of threats throughout the annual cycle. The impact of mortality during the nonbreeding season on individual breeding colonies is unknown but has important ramifications for conservation and management. In this study we used restriction site-associated DNA sequencing (RADseq) to provide 6614 genome-wide single nucleotide polymorphisms (SNPs) to investigate population genetic structure of northern fulmars using 127 individuals from six breeding colonies spanning the Atlantic. Additionally, birds of unknown breeding origin were sampled from two locations: (1) offshore in the Labrador Sea, and (2) the Baffin Bay-Davis Strait region (NAFO subarea 0), as bycatch in gillnets set for Greenland halibut (Reinhardtius hippoglossoides). We found weak genetic differentiation among breeding colonies, which we suggest reflects historical associations as well as contemporary gene flow among populations. Most bycatch birds were likely from nearby breeding colonies in the eastern Canadian Arctic, but the exact breeding origins were difficult to determine due to the lack of differentiation between colonies.

The impact of different assumptions about reproductive potential and recruitment on a Management Strategy Evaluation for the Greenland halibut stock in NAFO Subarea 2 and Division 3KLMNO

The impact of different assumptions about reproductive potential and recruitment on a Management Strategy Evaluation for the Greenland halibut stock in NAFO Subarea 2 and Division 3KLMNO

Does increased information about reproductive potential result in better prediction of recruitment?

The relationship between stock size and recruitment is an essential element in the understanding of the productivity of a population. However, predicting the number of recruits produced by a population has proven to be a difficult challenge. This may in part be a result of poor estimation of reproductive potential (RP). We determined if including increased information on reproductive biology in indices of RP results in better predictions of recruitment. We investigated some of the conditions that lead to better (or worse) recruitment prediction when more biologically complex indices of RP are used. Data from four populations in the Northwest Atlantic were examined: southern Grand Bank (NAFO Division 3NO) cod ( Gadus morhua ), Flemish Cap (NAFO Division 3M) cod, Newfoundland (NAFO Division 3LNO) American plaice ( Hippoglossoides platessoides ), and Greenland halibut ( Reinhardtius hippoglossoides ) (NAFO Subarea 2 + Division 3KLMNO). Stock–recruit models paired with complex indices of RP gave a better estimate of recruitment in slightly more than half of the tests conducted. When there were larger trends in the reproductive biology (maturity at age, sex ratio and egg production), more complex indices of RP were more likely to provide a better estimate of recruitment.

Review of the population structure and ecology of S. mentella in the Irminger sea and adjacent waters

Significant controversies exist over the three types of Sebastes mentella found in the Irminger Sea and adjacent waters. Preliminary genetic studies have given evidence for the existence of three distinct groups, characterized using several molecular genetic markers. The biological or ecological significance of these between-group differences has, however, not been evaluated. In the present paper, we review the life cycle of S. mentella in this area, based on published data. Spawning of S. mentella in the Irminger Sea takes place in a single area above Reykjanes Ridge. The larvae drift towards East Greenland from where they are carried to West Greenland (NAFO Subareas 0+1). Later they return to East Greenland where the main nursery area has been identified. There is evidence for a migration of juvenile fish from the nursery area into the open Irminger Sea, where many different cohorts spawn. We also compare these ecological data with the genetic results and we conclude that the observed genetic differences can be derived from possible genetic drift, selection or mostly from temporal variation (age dependency). which has also been reported for other species with as high longevity as S. mentella. We conclude that S. mentella in the Irminger Sea and adjacent waters comprises one single population.

Hydrographic Variability in the Waters of the Gulf of St. Lawrence, the Scotian Shelf and the Eastern Gulf of Maine (NAFO Subarea 4) During 1991-2000

Hydrographic Variability in the Waters of the Gulf of St. Lawrence, the Scotian Shelf and the Eastern Gulf of Maine (NAFO Subarea 4) During 1991-2000

Variability of the Water Properties in NAFO Subareas 5 and 6 During the 1990s

The variability in temperature and salinity of the waters on the northeast USA continental shelf and the Gulf of Maine during the 1990s is presented and compared to that during a previous period (1978–87). A general freshening of the surface waters in the Gulf of Maine and of the shelf waters in the Middle Atlantic Bight is documented. An increase in the inflow to the Gulf of Maine of cool, low salinity surface water from the Scotian Shelf during the 1990s was responsible for the freshening. Wintertime warming of the shelf waters in the southern part of the region was noted. The deep waters of the western Gulf of Maine also exhibited a warming during the 1990s. This warming is believed due to reduced winter convective cooling, caused at least in part, by the freshening of the surface layer which increased the stratification that inhibited convection.

Changes in the population of American plaice ( Hippoglossoides platessoides) off Labrador and northeastern Newfoundland: A collapsing stock with low exploitation

Changes in the population dynamics of American plaice off southern Labrador and eastern Newfoundland (NAFO Subarea 2 and Division 3K) for the period 1977–1994 were investigated. Since the mid 1980s the population has declined dramatically and by the 1990s the stock had essentially collapsed. A higher proportion of what remained of the stock was found in deeper and warmer water than had previously been observed, coincident with a period of unusually cold ocean conditions. During the period of the greatest reductions in population size, the proportion of older, spawning-age fish declined much more rapidly than the younger ages and this decline was accompanied by a slight decrease in mean size at age. Also associated with these observations were declining trends in both size and age at maturity. Although exploitation has always been low, the fishery for American plaice in NAFO Subarea 2 and Division 3K has been regulated since the early 1970s. For the period investigated the average annual commercial exploitation rate was less than 2% with negligible bycatch in other fisheries. We conclude, therefore, that the collapse of this stock was not a result of fishing mortality. The causal mechanism for the decline remains unclear although unusual environmental conditions during the period continue to be investigated in relation to the observed changes in this population.

Life history strategies of the squid,Illex illecebrosus,in the Northwest Atlantic

Resume Time series (1965-1985) of lllex illecebrosus catch and morphomctric data from the Northwest Atlantic were analysed to describe geographic variability in population structure. The areas studied were NAFO sub-areas 3 to 6, which range from Newfoundland to the northeastern USA shelf. Population components, reflecting seasonal spawning groups, were identified based on analysis of length frequency data. Components 3 and 4 represent two prominent life cycles: the summer spawners and winter spawners respectively. Components 1, 2, and 5 do not represent different life cycles, but result from the capacity to shift between life cycles by prolonging (or shortening) the life span. The presence of up to five components in the southern area illustrates a life history strategy involving protracted spawning and complex population structure. There was clear geographic variability in annual catch, with fluctuations being most extreme in the most northem area. Annual catch levels in al1 areas were significantly correlated with the abundance of the winter-spawning component, as represented by the number of squid within samples which belong to component 4. Population structure in the most northem area was simplest and catch levels therefore were most dependent on the highly migratory winter-spawning component. This leads to greater catch variability in the most northern area than in the other areas. The advantages of good feeding conditions may compensate for the risks associated with long-range migrations, especially recruitment failure. Life history strategies involving migratory and non-migratory population components limit the risk of recruitment failure. The overall resultant life history strategy for Illex illecebrosus is one that ensures survival of the species by stabilizing recruitment in at least one (southern) area through protracted spawning, complex population structure and interaction of spawning components.

Estimation of Age and Growth of Northern Shrimp (Pandalus borealis) in Davis Strait (NAFO Subareas 0+1) Using Cluster and Modal Analyses

Shrimp (Pandalus borealis) length frequency distributions obtained during research surveys in Davis Strait (NAFO Subareas 0+1) from 1983 to 1987 were analyzed for age and growth. Samples were combined within year on the basis of their similarity using cluster analysis. Modal analyses were performed for males only, separating the distribution mixtures into normal components which were interpreted as ages 1 to 6, inclusive. Mean carapace lengths at these ages were estimated at 8.4, 12.3, 15.7, 18.5, 20.6 and 22.7 mm, respectively. Females were separated at ages 7 and 8+ on the basis of biological characteristics with mean lengths of 24.9 and 26.3 mm. A comparison of results from Davis Strait with those reported from other areas in the Northwest Atlantic showed increased longevity and slower growth in the north.

An eighteenth century commercial length-frequency sample of Atlantic cod, Gadus morhua, based on archaeological data

A length frequency was developed from measurements of 174 cleithra of cod ( Gadus morhua) which had been recovered from the wreck of a fishing schooner lost on the coast of Nova Scotia during the 1750s. The fish were probably part of a commercial catch, most likely taken by handlines on the offshore banks in NAFO Divisions 4VsW. Their estimated lengths ranged from 52 to 120 cm with a mean of 89.1 cm. While modern hook-caught cod from NAFO Subarea 4 are usually much smaller than those lost on the wreck, fish of a similar size are still occasionally caught. Indeed, current longline catches of Grand Bank (Divisions 3NO) cod are of much larger fish. We conclude that, while the average size of northwest Atlantic cod may have decreased under modern fishing pressure, specialised fisheries can still target fish of similar sizes to those caught 200 years ago.

Distribution, Growth and Food Habits of the Atlantic Wolffish (Anarhichus lupus) from the Gulf of Maine-Georges Bank Region

Distribution, Growth and Food Habits of the Atlantic Wolffish (<i>Anarhichus lupus</i>) from the Gulf of Maine-Georges Bank Region

Weight-length relationships of roundnose grenadier ( Coryphaenoides rupestris Gunn.) in different areas of the North Atlantic

The weight-length relationships of roundnose grenadier ( Coryphaenoides rupestris Gunn.) caught in different parts of the northwest Atlantic were determined and compared with relationships reported previously for various areas of the North Atlantic. The results indicate that this species is lighter at length in NAFO Subareas 0 + 1 and the north Mid-Atlantic Ridge area than in either the northwest or northeast Atlantic. Roundnose grenadier in the northwest and northeast Atlantic have approximately the same weight-length relationships.

Review and Assessment of the Georges Bank and Gulf of Maine Haddock Fishery

The Georges Bank and Gulf of Maine haddock resource and fishery is reviewed. Nominal catches for Georges Bank averaged 46,000 metric tons annually during 1935-60 and then increased to a peak of 150,000 tons in 1965 as Canadian and distant water (European) fleets entered the fishery. Catches subsequently declined to an average of 5,000 tons during 1974-76 under quota and incidental catch limitations and then increased rapidly to an average of 21,000 tons in 1978-79. Nominal catches for the Gulf of Maine averaged 5,000 tons during 1935-66, declined to less than 1,000 tons during 1972-74 and increased to an average of 5,000 tons in 1978-79. Minor recreational catches have also been reported from the western Gulf of Maine in recent years. Total stock size (age 2 and older haddock) for Georges Bank, determined from virtual population analysis, averaged 140 million fish (153,000 tons) during 1935-60, increased to 530 million fish (427,000 tons) in 1965 and declined precipitously to 8 million fish (22,000 tons) in 1972. Subsequently, there was a substantial increase in stock size due to recruitment of the 1975 year-class. The 1978 year-class appears to be comparable in size to that of 1975. Instantaneous fishing mortality (F) for age 3 and older fish averaged 0.44 during 1935-60, increased to a peak of 0.79 in 1966 and subsequently declined as abundance decreased and fishing effort was diverted to other species. Trends in abundance and mortality evidenced by data from research vessel surveys since 1963 have been generally consistent with those indicated by virtual population analysis. Variability in growth of Georges Bank haddock during 1931-65 and pronounced <i;,anges in the late 1960's and early 1970's appear primarily attributable to changes in abundance. Reduction in spawning stock biomass during the late 1960's and early 1970's was associated with low recruitment and increased variability in year-class size. Trends in abundance for the Gulf of Maine were similar to those observed for Georges Bank, although discrepancies were evident in relative strengths of recent year-classes. Fig. 1. Georges Bank and Gulf of Maine areas with place names and boundaries of divisions mentioned in the text. (Crosshatched areas are subject to seasonal closure.) (NAFO Subarea 5), although substantial quantities were also taken on Browns Bank (NAFO Division 4X) and areas farther eastward (Fig. 1). SUbsequently, the

A Procedure for Evaluating the Food Biomass Consumed by a Fish Population

An application of the Ursin fish growth theory for evaluating the food biomass consumed by a fish population is proposed. In this procedure the total catabolism of a fish is treated as dependent on the level of available food. This is the major advantage of the procedure in comparison with that based on the most frequently used Winberg fish growth theory, in which the total catabolism rate is assumed to be independent of the available food level. The Atlantic cod (Gadus morhua) population inhabiting the southern Gulf of St. Lawrence (NAFO subarea 4T) in 1978 is considered in order to illustrate the procedure. The food biomass consumed by the cod population in this area and period is evaluated to be 0.727 million tonnes (the food consumption of the 0th cod age-group is not included). The uncertainty in the estimate of this food biomass due to uncertainties in the input parameters for the procedure is estimated to be in the range of 20% (standard error). Possible ways of improving the results of the procedure are discussed in the light of uncertainties in the input parameters and the sensitivity of the model upon them. It is concluded on the basis of a sensitivity analysis performed for the numerical example of procedure and the foraging theory for fish that the assumption introduced by Winberg can, in certain cases, introduce considerable bias to the procedure results.Key words: fish, food consumption, growth, physiology, bioenergetics, cod, model, sensitivity analysis