Northern Stock Research Articles

Did over-reliance on commercial catch rate data precipitate the collapse of northern cod?

Abstract It has been suggested that a number of “lessons” can be learned from the collapse of the northern cod stock off Newfoundland and Labrador. However, not all purported lessons have been validated with available data. One lesson is thought to be that over-reliance on commercial catch rate data and an incorrect assumption regarding the functional relationship between catch rate and population size were major contributors to overestimating stock size, precipitating the collapse. The current study describes calibration approaches used in assessments, and evaluates alternative functional relationships between commercial catch rates and stock size. In addition, historical population size is re-estimated using only research vessel data and compared with estimates obtained based on both commercial catch rate and research vessel data. Calibration with commercial catch rate contributed to overestimating stock size in some years, but there is no evidence that the assumed functional relationship between commercial catch rate and population size was a significant factor in the collapse.

Hilali Narratives from Southern Arabia

The Strat Bant Hildl is usually related to Syrian storytellers, Egyptian poets, or Maghrebi fddwi. Information about Hilali traditions in southern Arabia the area of our interest is very scarce. Fifteen years or so ago, when starting re search on Hilali epic tales and poetry in the Yemen, as a working hypothesis I assumed the persistence of a geographical continuity of Hilali traditions along the Nagd right into southern Arabia, in an imaginary line which embraces the eastern part of the Yemen and then, going further east, skirts the southern bor ders of the Rubc al-Hali desert. Scholars and travellers such as C. Landberg and B. Thomas have confirmed the presence of traditional Hilali tales in these re gions. The Banu Hilal are considered as belonging to northern stock, through a genealogical line which connects them to cAdnan, but some Yemeni claimed true Hilali origin: they were the descendants of those people who re mained behind when the Banu Hilal abandoned the country due to a prolonged period of famine (or even after the Marib dam broke!), thus beginning that eventful migration which ended in North Africa. Travellers' reports and infor mation collected on the spot both locate the territory of these 'forgotten' in the area surrounding the Ramlat al-Sabcatayn desert. The living here are different under certain aspects from their neighbours, who emphasise that they are Banu Hilal and indicate Wadi Marhah as their ter ritory. Historians have generally been interested in the Yemen of the great of the plateau and much less in the nomads. It is therefore hardly surprising not to find any mention of the Nisiyyln and other Hilalis, tribes of marauders as H. St.-J. Philby described them. No specific studies have been carried out on Hilali traditions in southern Arabia, but these traditions must undoubtedly have been important if B. Thomas went so far as to uphold that Bani Hillal is the fount of the whole folk-lore of the southern desert.2

Spain's North Atlantic swordfish fishery

Abstract The great growth of the Spanish swordfish fleet at the beginning of the 1990s has consolidated its position as the main northern stock swordfish producer, followed far behind by the USA, Canada and other EU countries. The aim of this paper is to analyse the determining institutional and economic factors in said fishery. We study the management instruments, placing special emphasis on the pertinent Spanish regulations and describe in detail the technical characteristics of the fleet, the fishing effort and the landings. We also carry out estimations of the revenues, costs and total income generated by the fleet. The results show the economic profitability of the fishery, with incomes which have increased, on average, by 7% in the last 15 years.

Capelin are good for cod: can the northern stock rebuild without them?

The stock of northern cod (Gadus morhua) off Newfoundland and Labrador is at its lowest level in recorded history, with no rebuilding of northern spawning aggregations since the fishing moratorium in 1992. Cod diet was historically dominated by capelin (Mallotus villosus), which have been scarce in the northern areas since 1990. Using the study areas Hawke Channel and Trinity Bay within the historical northern cod range, and Placentia Bay (south coast), we examine growth, condition, and reproductive potential with respect to capelin diet in 18 000 cod sampled primarily in January and June of the years 1996-2000. Overall diet weights differed among areas and seasons (Placentia=Hawke>Trinity in January; Placentia>Trinity=Hawke in June). However, just 7 of 3383 cod stomachs (0.2%) from Hawke contained capelin (PFI=0). In contrast, 10% of cod of ages 3-7 in Placentia and Trinity Bays preyed on capelin and overall capelin partial fullness indices (PFI) were 0.2-0.4. Capelin PFIs were correlated with an index of availability (potential contact of capelin within 40 km of cod) calculated from acoustic surveys. Seasonally adjusted cod liver condition was strongly associated with capelin availability (p Trinity≫Hawke).

Population structure ofChlamys islandicain the Northeast Atlantic — northern stocks compared with a southern relict population

Abstract To gain a better understanding of the genetic relations that may exist between populations of Chlamys islandica in different regions of the northern Atlantic, the geographic range of earlier studies was extended to include populations sampled further east (Kap Kanin in Russia) and west (Breidarfjordur on Iceland), plus a relict population from the southwest coast of Norway (Fauskangerpollen). The patterns of variation that were found at selected allozyme loci support the suggestion that populations of C. islandica in the Northeast Atlantic are genetically structured. The relict population from Fauskangerpollen was genetically most distinct from any of the other populations.

Interpreting the collapse of the northern cod stock from survey and catch data

Interpreting the collapse of the northern cod stock from survey and catch data

A possible separation between a northern and a southern stock of the northeast Atlantic blue whiting

Blue whiting ( Micromesistius poutassou) in the northeast Atlantic system, probably consists of several stocks. For assessment purposes two main components, one spawning along the slope north of and one along the slope south of the Porcupine Bank, have been assumed. The Porcupine Bank area has been considered a transition zone. We address the question of the existence of a separation line between the southern and the northern stock. Our hypothesis is that this can be explained from the drift patterns of the larvae in such a way that the northern stock larvae tend to drift northwards, and the southern ones southwards. To check this, a Lagrangian transport model has been used in connection with a hydrodynamic circulation model. The circulation model has been run with realistic forcing for 20 separate years (1976–1995). For each year particles assumed to simulate blue whiting larvae have been transported from the spawning grounds using the transport model. Based on the modelled drift a separation line north of Porcupine Bank has been found. The line shows a large interannual variability indicating a mix between the two stocks.

鱗の第１輪径からみた若狭湾西部海域におけるマダイ群の移出入

The present paper deals with the changes in the radius composition of the first ring on the scale with age of red sea bream Pagrus major, and estimates its migration, or immigration and emigration patterns in Western Wakasa Bay, using fish 1 to 5 years of age in the 1991 year group and fish l to 4 years of age in the 1992 year group.Scale radius (Rin mm) was related to fork length (FL in mm) in each year group as expressed by the following equations, 1991 year group: ln FL=1.047ln R+3.4641992 year group: ln FL=1.041ln R+3.473In the compositions of the first ring radii on the scales in younger age-group (fish less than 3 or 4 years), it was revealed that the percentage occurrences of those with the small first ring radius (northern stock) increased with their ages, while the large first ring radius (southern stock) decreased. Based on the regional differences in the size of the first ring radius on the scale of l year-old fish, it is suggested that the northern stock migrates into Western Wakasa Bay and possibly mixes with local stock (the medium first ring radius) in the Bay. Based on the change in the estimated catch in numbers by age and three types of radius (large, medium and small radius) in the 1991 year group, at least about 30% to 70% of red sea bream at 4 years of age might participate in their immigration or emigration in Western Wakasa Bay.

Density-dependent growth and sexual maturity of silver hake in the north-west Atlantic

Stock abundance was the most important predictor of sexual maturation of age 2 and 3 silver hake in the north-west Atlantic between 1973–1990. Growth at ages 1 and 2 in the southern stock was significantly and negatively correlated with stock abundance (r2>0.56, P<0.01). Sexual maturity may be mediated through competition and growth during the first and second years of life. In the northern stock, growth and stock abundance was not significantly correlated (P>0.05). Here, increased sexual maturity at ages 2 and 3 during 1973–1990 may have occurred without increased somatic growth, already near its maximum, due to the relatively cooler water temperatures of the Gulf of Maine. Logistic regression models indicated that maturation is dependent on age, stock density and an age-density interaction.

Comment: Scientific inquiry and fish stock assessment in the Canadian Department of Fisheries and Oceans

Contrary to the argument of Hutchings et al. (1997), DFO invited independent examination of the assessment of the northern cod stock and followed the advice of the Independent review of the state of the northern cod stock. Rather than suppressing information about the importance of high fishing mortalities in the decline of Atlantic groundfish, DFO stock status reports have highlighted its importance. DFO encouraged staff with a wide range of views to testify at the major BCUC inquiry. DFO's peer review system for stock assessments involves external reviewers who see the data and know the conclusions reached before DFO managers. We consider that the peer review process in place for Canadian fish stock assessments is as good or better than other systems in use elsewhere in the world.

The Atlantic Canada Resource Management Catastrophe: A Predator-Prey consideration

As the northern cod fishery constitutes the most important fishery of the Canadian Atlantic coast, I shall focus my discussion on it. Many important factors contributing to the failure of the northern cod fishery have been identified. For example, the Report of the Task Force on Income and Adjustment in the Atlantic Fishery chaired by Richard Cashin (1993) gives half a dozen reasons for the collapse of the northern cod stock. They are (1) overly high Total Allowable Catch (TAC) levels due to over-optimistic scientific projections, inadequate understanding of the stock dynamics and inaccurate data on commercial fishing activity; (2) underreporting of catches and misleading data for management; (3) destructive fishing practices such as highgrading, discarding and dumping; (4) foreign overfishing on the Nose and Tail of the Grand Banks; (5) failure to control expansion of fishing effort due to the demands of a processing sector with excess capacity and failure to minimize the adverse impact of various fishing gear technologies; and (6) unforeseen ecological changes, including cooling water temperature since the mid-1980s, changes in water salinity, and shifting predator-prey relationships, particularly among seals, capelin and cod. I shall concentrate my discussion on the predator-prey consideration. In doing so, I do not mean to suggest that the seal is the only main culprit. Far from it, I agree that it is a combination of the above factors that caused the current crisis. Given the limitation of my presentation, I could only consider a small piece of the puzzle. Obviously, seal and cod have coexisted and been harvested for centuries. Why should it be an issue now? Even the biologists cannot determine for certain whether or not the seal is a direct predator of cod. However, the matter must be understood in the context of a broader predator-prey relationship involving seal, cod, capelin and perhaps other species. The problem of uncertainty that Gordon Munro alluded to in his introduction in the Calgary meeting may also be attributed to imperfect knowledge about the ecological system. After examining some data, I am convinced that the collapse of the northern cod stock is, in part, due to a

Habitat Use and Movements of Two Ecotypes of Translocated Caribou in Idaho and British Columbia

Two woodland caribou (Rangifer tarandus caribou) ecotypes, mountain and northern, were translocated to the southern Selkirk Mountains in northern Idaho (U.S.A.) to augment a remnant subpopulation. The translocation resulted in an additional subpopulation that used the general area of the release site. The mountain ecotype stock exhibited patterns of movement and habitat use similar to those of the resident subpopulation. The northern ecotype stock exhibited more variable habitat use, especially in the first year after translocation. Dispersal of the northern stock was not as extensive as that of the mountain stock. Fourteen of 22 caribou from the northern stock and 6 of 18 caribou from the mountain stock died during the 3‐year period after the release. Our results suggest that when donor subpopulations must be used that do not closely compare with resident subpopulations extinct or extant, larger numbers of individuals may be needed to establish a self‐sustaining population.

Empirical and theoretical analyses of correction of time-series bias in stock-recruitment relationships of sockeye salmon (Oncorhynchus nerka)

Using data from 30 sockeye salmon (Oncorhynchus nerka) stocks and Monte Carlo simulations, we examined the importance of time-series bias on estimates of optimal harvest rate, optimal escapement, and sustainable yield. We compared the performance of the least-squares procedure for fitting a Ricker curve with an existing bias-correction method. Simulations showed that the effect of time-series bias is greatest for low-productivity stocks that exhibit a high degree of autocorrelation among residuals of the stock-recruitment relationship. A strong inverse empirical relationship between autocorrelation and stock productivity among the 30 stocks suggests that time-series bias is a more important concern for low-productivity northern stocks than for more productive southern stocks. The corrected method reduced bias in optimal escapement estimates under a limited set of conditions but at the price of increased variance in the estimates. For a constant escapement goal policy, using the bias correction thus resulted in sustainable yields slightly lower than or equal to expected values for 28 of the 30 stocks compared with yields obtained using the standard least-squares estimation method. We demonstrate the value of using a decision theoretic approach to evaluate the performance of estimation methods.

Molecular diversity and derivations of populations of Silene acaulis and Saxifraga oppositifolia from the high Arctic and more southerly latitudes

AbstractA survey of allozyme diversity within and between populations of Silene acaulis from Spitsbergen, Norway, Iceland and Scotland, showed that populations from the high Arctic (Spitsbergen, &gt; 76°N) contained high levels of diversity and were genetically similar to populations from more southern locations. Indirect measures of gene flow (Nm), calculated from Wrigh's F indicated that there had been extensive gene flow between Spitsbergen and some Norwegian populations. A restriction site analysis of chloroplast DNA (cpDNA) in S. acaulis revealed that all populations contained a single identical cpDNA haplotype, except one population from Norway which also contained a second haplotype. In contrast, five different cpDNA haplotypes were distinguished in a more limited survey of cpDNA variation in Saxifraga oppositifolia, with all five haplotypes present in one of two Spitsbergen populations surveyed. The contrasting cpDNA results for the two species suggest that whereas high‐Arctic populations of Silene acaulis have most likely been derived from immigrants which arrived from the south after the last glacial period, high‐Arctic populations of Saxifraga oppositifolia may be derived, in part, from ancient northern stocks which survived the last glaciation in high‐Arctic refugia.

Distinguishing between resident and migrating Atlantic salmon (Salmo salar) stocks by genetic stock composition analysis

The possibility of using the genetic stock identification (GSI) method to distinguish between individual Atlantic salmon (Salmo salar) stocks and stock groups in Finnish catches was studied. In the Baltic Sea, the Atlantic salmon is a target of a mixed-stock fishery, and information about stock composition would be valuable for the management of the species. The salmon catches on the Finnish west coast consist of two seasonally variable components: a group of northern stocks migrating through the area to the Baltic main basin and the resident Neva salmon. The migratory component includes two endangered wild stocks (Tornionjoki and Simojoki). The allele frequency differences at four polymorphic loci among the stocks allowed reliable catch composition estimates to be made of the migratory and resident components; one stock (Oulujoki) from the northern group could also be identified with reasonable accuracy. Northern migrating stocks accounted for over half the catches at the time of this study. The estimate of natural (nonhatchery) stocks was very low (3% in total).

Survival of Northern Atlantic Cod (Gadus morhua) Eggs and Larvae when Exposed to Ice and Low Temperature

Freeze resistance of eggs and larvae of Atlantic cod (Gadus morhua) from the northern cod stock was investigated to determine whether ice contact could affect survival during the spring spawning season off Newfoundland. Egg and larval homogenates did not appear to contain antifreeze proteins (mean freezing points −0.78 and −0.88 °C, respectively). However, cod eggs did not freeze at −1.8 °C in icy aerated seawater, could be undercooled to −4.0 °C in ice, and froze at temperatures between −4.1 and −1 7 °C; freeze resistance depended on the integrity of the chorion. Larvae withstood undercooling to −1.8 °C, provided they were not brought into direct contact with ice crystals, if directly touched with ice, larvae froze at −1.36 °C (feeding stage) or −1.34 °C (yolk-sac), approximately 0.5 °C lower than would be expected from the freezing temperatures of their body fluids. The nature of their external epithelium and delayed development of sensitive gill structures below 0 °C may contribute to larval freeze resistance. Cod eggs and larvae are found in spring off Newfoundland and Labrador, when sea temperatures can be as low as −1.8 °C and ice cover extensive. While cod eggs are remarkably freeze resistant, such environmental conditions may cause freezing mortalities in larval cod.

Influence of Long-term Changes of Sea-Surface Temperature on the State of Some Fish Stocks in the Northwest Atlantic

The changes in spawning biomass of the northern stock cod in Canadian waters and cod biomass off West Greenland were compared with the changes of sea-surface temperatures (SST)in the Irminger Sea.The correlation between variations of SST and cod biomass during the period 1956–88 in these areas indicated the influence of climatic changes on the status of the spawning stock of cod in the Newfoundland area and the cod stock at West Greenland. Similar correlations were observed in the variations of SST during the period 1977–88 in the Scotian Shelf area and the status of the silver hake stock. Introduction Over the recent 30 years, considerable changes in the status of stocks of some commercial fish species in the Northwest Atlantic have been reported. The changes in the biomass of particularly the northern spawning stock of cod off Newfoundland (FO’S’CLE, 1988), cod stock at West Greenland (Schumacher, MS 1988) and the silver hake stock on the Scotian Shelf (Fanning et al. MS 1987; Noskov, MS 1987) have been of significant interest in recent years. In the late-1970s and early-1980s these stocks were reduced to their minimum levels, followed by marked increases in the mid-1980s. There have been differing viewpoints concerning the causes of these changes. While various abiotic and biotic factors are often considered to have effects on the status of the stocks, one of the causes is also thought to be the introduction in 1977 of the Extended Jurisdiction of Coastal States to 200-miles from the coastline and the subsequent fishery regulatory measures and fishing practices. The overall effect of such factors are difficult, if not impossible to evaluate, however, consideration of individual factors are often possible and practical. The present report considers the relationship of one environmental parameter, water temperature, in relation to the status of these three fish stocks. Materials and Methods Mean monthly sea surface temperatures (SST) from the centres of each 5° quadrants of latitude and longitude on the Scotian Shelf (40–45°N, 60– 65°W) and in the Irminger Sea (55–60°N, 30–35°W were obtained from the Hydrometeocenter of the Union of Soviet Socialist Republics. Information on the status of the three stocks was obtained from published literature. Silver hake biomass estimates were from Fanning et al. (MS 1987) and Noskov (MS 1987), while the biomass estimates of the northern spawning stock of cod off Newfoundland were from FO’C’SLE (1988) and the West Greenland cod stock were from Schumacher (MS 1988) and other papers. The SSTs are considered as indexes reflecting the interaction of oceanolographic systems. The systems relevant to this study consist of: the admixture of warm Gulf Stream waters and cold waters of the Labrador Current in the Nova Scotian Shelf area; warm waters of the North Atlantic Current merging with the Irminger Current and cold polar and Labrador waters in the Irminger Sea and West Greenland areas. Integral curves of the water temperature anomalies at the sea surface were therefore prepared. This technique is widely accepted in studies of global variations of the oceanolographic and hydrometeorlogical factors in the North Atlantic (Zverev, 1972; Girs, 1971). The integral curves are good for identification of intensifications (when positive values of anomalies are recorded), weakening (when negative values of anomalies are recorded) or stabilization (when small departures are recorded in the anomalies) of the SST. The increase of the sum of water temperature anomalies on the Scotian Shelf is considered to be the result of intensification of the Gulf Stream influence (approaching closer to the Shelf) while the decrease is assigned to increased influence of the cold Labrador Current. Similarly, the rise of the water temperatures in the Irminger Sea can be attributed to the increased effect of the warm Irminger Current and the movement of the subpolar front to the north and west, while the drop of temJ. Northw. Atl. Fish. Sci., Vol. 14: xx–xxx 2 J. Northw. Atl. Fish. Sci., Vol. 13, 1992 TABLE 1. Change of sum of SST anomalies in the Irminger Sea from 1977 to 1988. Month 1977 1978 1979 198

Predicting Recruitment Variation from Year Class Specific Vertebral Counts: An Analysis of the Potential and a Plan for Verification

Recruitment prediction has been an elusive and seemingly unobtainable goal with no entirely satisfactory general approach yet available. I propose the use of meristic variation, traditionally applied to problems associated with stock discrimination studies, as a new method to predict recruitment variation. The approach is evaluated using literature data on year class strength (YCS) and year class specific average vertebral counts (VS), two apparently interrelated variables that are affected by environmental factors operating during the early life history. Three marine stocks at the southern limit of their species geographic range (Georges Bank haddock (Melanogrammus aeglefinus), North Sea Atlantic cod (Gadus morhua), and North Sea Atlantic herring (Clupea harengus hargenus)) and one stock at its northern limit (Pacific herring (Clupea harengus pallasi)) generally conformed to the prediction of a positive relationship between YCS and VS for southern stocks and a negative relationship for northern stocks. Exceptions to these patterns were found among stocks showing low temporal variability in recruitment or for stocks whose year class formation is not linked to environmental factors that establish the vertebral count of a year class. The approach adopted is consistent with the growing initiative of focusing on characteristics of the survivors of a population to provide insight into recruitment mechanisms.

Incubation of salmon eggs and rearing of alevins: Natural temperature fluctuations and their influence on hatchery requirements

The eggs and alevins of Atlantic salmon ( Salmo salar L.) are normally reared in Scotland using surface water in open flow systems. The literature indicated that incubation temperatures should generally be in the range 4°–11°C. A strategy that might lead to most success would be to keep green eggs at 6°C and then reduce the temperature to 4°C during subsequent development. Genetic variations between races of salmon in different river systems may partly account for differences in reported incubation times. Several northern stocks are known to be cold-adapted and it seems clear that standardised incubation regimes are inappropriate in the absence of standardised fish and water quality. The cumulative ambient water temperatures at four Scottish hatcheries were shown to approximate those required by the industry, although some very low temperatures were regularly experienced. The technology for temperature control is generally available, but has not been widely used. To be most succussful it should be geared towards producing fish ready for first feeding by the end of April, as natural temperatures are increasing rapidly (10°–14°C), so that an open flow system can be used for feeding. A review of the literature showed that temperature effects should not be considered in isolation. Low pH, resulting from acid rain and snow-melts, was also recognised as a potential problem as was subsequent metal pollution. To be most effective, recycle systems should be designed to control both temperature and pH.

Influence of parental stock and incubation temperature on the early development of coho salmon (Oncorhynchus kisutch) in British Columbia

Coho salmon (Oncorhynchus kisutch) stocks in British Columbia spawning from October to April were surveyed for variation in developmental characteristics at incubation temperatures from 1.5 to 15 °C. There were no trends in embryo or alevin survival rates associated with spawning time or spawning temperature. The highest embryo and alevin survival rates occurred at 4 or 5 °C and complete mortality generally occurred at 14 or 15 °C. Vancouver and Queen Charlotte Island stocks had lower survival rates at 1.5 and 2 °C than did mainland stocks. Time to 50% hatching and 50% emergence varied inversely with incubation temperature. Alevin hatching time for the Pallant Creek stock on the Queen Charlotte Islands was later than for all other stocks. Stocks had different trends in alevin and fry length and weight with respect to incubation temperature. Northern stocks tended to be more efficient than southern stocks at converting yolk to body tissue at 1.5 and 2 °C, as were mainland stocks compared with island stocks.