Can changes in length-at-age and maturation timing in Scotian Shelf haddock (Melanogrammus aeglefinus) be explained by fishing?

2010 ◽  
Vol 67 (5) ◽  
pp. 854-865 ◽  
Author(s):  
Anna B. Neuheimer ◽  
Christopher T. Taggart
Keyword(s):  
Thermal Constant ◽  
Melanogrammus Aeglefinus ◽  
Fish Length ◽  
Age At Maturity ◽  
Scotian Shelf ◽  
Early Maturation ◽  
Stock Biomass ◽  
Age Variation ◽  
Size At Age ◽  
Haddock Melanogrammus Aeglefinus

Factors affecting size-at-age in fish populations include temperature and fishing where the latter can represent a strong selective force on size-at-age variation through changes in population growth and maturation. Over the past three decades, Scotian Shelf haddock ( Melanogrammus aeglefinus ) exhibited declines in maturation timing and mature fish length-at-age. Here, we examine these declines with respect to temperature, stock biomass, and fishing. We employ the thermal integral (growing degree-day, GDD, °C·day) to examine the variation in length-at-age (length-at-day, LaD, cm) and maturity (age-at-50%-maturity) that is attributable to temperature. Unexplained variation in LaD and age-at-50%-maturity remains and is characterized by declines in the LaD-at-GDD regression parameters and the thermal constant for maturity with increasing year-class. We find no significant correlation between the temperature-independent declines in LaD and stock biomass. The combination of high fishing mortality (favouring early maturation) and sustained harvesting of large fish (fast-growing, late-maturing individuals) offers the simplest explanation for the systematic decline in inferred growth and age-at-maturity for Scotian Shelf haddock. These results are consistent with other exploited populations and recent laboratory experiments quantifying the effects of fishing on size-at-age and age-at-maturity.

Dispersal of early life stage haddock (Melanogrammus aeglefinus) as inferred from the spatial distribution and variability in length-at-age of juveniles

1999 ◽  
Vol 56 (12) ◽  
pp. 2350-2361 ◽  
Author(s):  
Nancy L Shackell ◽  
Kenneth T Frank ◽  
Brian Petrie ◽  
David Brickman ◽  
Jennifer Shore
Keyword(s):  
Early Life ◽  
Life Stage ◽  
Circulation Model ◽  
Early Life Stage ◽  
Melanogrammus Aeglefinus ◽  
Bay Of Fundy ◽  
Shelf Area ◽  
Scotian Shelf ◽  
Frequency Distributions ◽  
Haddock Melanogrammus Aeglefinus

In southwestern Nova Scotia, haddock (Melanogrammus aeglefinus) spawning is centered on Browns Bank where the variability of a partial gyre influences the distribution of eggs and larvae. An unknown proportion of each year-class is advected northward to the Bay of Fundy. We examined the variability in length at age 2 as an index of retention during early life. We assumed that early life stages that are retained in the Scotian Shelf area grow more slowly, while those that are advected into the Bay of Fundy grow more quickly. An optimization program was used to estimate the proportions of Scotian Shelf and Bay of Fundy sized components in length at age 2 bimodal frequency distributions for year-classes 1968-1993. The median proportion of Scotian Shelf sized fish was 0.89. A physical circulation model showed that the majority of particles released on Browns Bank drifted towards the Bay of Fundy. Results of the physical model and the size-based index differ partly because the former predicts the fate of passive particles, while the latter is an integrated measure of the proportion of fish retained and surviving. Survival is associated with high wind stress (r = -0.5, p = 0.011, n = 25) implying a higher probability of survival of those retained in the Scotian Shelf region.

Alimentary tract parasites of haddock (Melanogrammus aeglefinus L.) on the Scotian Shelf

1981 ◽  
Vol 59 (12) ◽  
pp. 2244-2252 ◽  
Author(s):  
J. S. Scott
Keyword(s):  
Alimentary Tract ◽  
Parasite Prevalence ◽  
Melanogrammus Aeglefinus ◽  
Bay Of Fundy ◽  
Scotian Shelf ◽  
Young Of The Year ◽  
Parasite Complex ◽  
Haddock Melanogrammus Aeglefinus ◽  
Hysterothylacium Aduncum ◽  
Biological Tags

Nineteen species of alimentary tract (including gall and swim bladders) parasites were found in haddock (Melanogrammus aeglefinus) on the Scotian Shelf, of which eight species were new Canadian records for haddock. Prevalence ranged up to 82.3% for Hysterothylacium aduncum and 70.9% for Echinorhynchus gadi, the most abundant parasites, with Lepidapedon rachion and Echinorhynchus gadi showing highest intensities (14.9 and 76.5, respectively). Prevalence decreased from summer to winter, was not related to sex of host, but showed geographical variation characterizing different geographical areas. The Bay of Fundy showed higher nematode and lower trematode abundance than the offshore Scotian Shelf which showed general clines in abundance of several species from southwest to northeast. There was no evidence of growth-related change in parasite prevalence in adult fish, but the parasite complex of young-of-the-year haddock indicated planktonic feeding, in contrast with benthic feeding in the adult. Site specificity within the alimentary tract was shown by several species. Echinorhynchus gadi changed its site seasonally. Lepidapedon rachion showed size differentiation in the gut, smaller trematodes occupying more anterior sites than larger. Only two parasite species offer prospects as biological tags, L. rachion and Myxidium bergense, but all may provide evidence of ecological, behavioral, seasonal and developmental changes in the host.

Reproductive Biology of Southwest Scotian Shelf Haddock (Melanogrammus aeglefinus)

1989 ◽  
Vol 46 (S1) ◽  
pp. s153-s170 ◽  
Author(s):  
K. G. Waiwood ◽  
M.-I. Buzeta
Keyword(s):  
Body Weight ◽  
Reproductive Biology ◽  
Seasonal Changes ◽  
Maximum Size ◽  
Melanogrammus Aeglefinus ◽  
Maturation Stage ◽  
Peak Activity ◽  
Gonad Weight ◽  
Scotian Shelf ◽  
Haddock Melanogrammus Aeglefinus

Information on the reproductive biology of Southwest Scotian Shelf haddock (Melanogrammus aeglefinus) (NAFO Division 4X) is presented including geographic distribution by maturation stage, timing of maturation, seasonal changes in gonad weight, spawning distribution in relation to environmental factors, and fecundity at length, weight, and age. Haddock were found to spawn on Browns, Baccaro, LaHave, and Roseway Banks over sand/gravel substrates. Spawning fish were found in a narrower and colder temperature range than were fish of other maturity stages. Spawning fish were found from April to August with peak activity occurring from April to June. Testes peaked in weight in February and March when they accounted for 1–2.2% of body weight while ovaries reached their maximum size (3.1–12.5% of body weight) from late March to mid-May. The length at 50% maturity varied over the period 1970–85 and these changes were correlated with changes in population biomass. There were no significant differences in fecundity/length relationships with area or year (1983–86) but fecundity for a given size decreased over the spawning season.

Density-dependent habitat selection by juvenile haddock (Melanogrammus aeglefinus) on the southwestern Scotian Shelf

1995 ◽  
Vol 52 (5) ◽  
pp. 1007-1017 ◽  
Author(s):  
C. Tara Marshall ◽  
Kenneth T. Frank
Keyword(s):  
Habitat Selection ◽  
Local Density ◽  
Population Analysis ◽  
Melanogrammus Aeglefinus ◽  
Model Parameters ◽  
Total Abundance ◽  
Scotian Shelf ◽  
Density Dependent ◽  
Density Dependent Habitat Selection ◽  
Haddock Melanogrammus Aeglefinus

Positive correlations between total abundance and indices representing distributional area have been reported for several marine fish stocks. Different indices can produce different results for the same stock and many indices scale positively with total abundance. We describe an alternative approach to modelling the distributional response to variation in total abundance using data for juvenile haddock (Melanogrammus aeglefinus) from the southwestern Scotian Shelf. Annual bottom trawl surveys having a stratified random design were used to estimate the local density of haddock age 1 and 2 in each strata. Estimates of total abundance-at-age were obtained from sequential population analysis. The relationship between local density and total abundance-at-age was described for each strata using an exponential model with a Poisson error structure. Systematic variation among strata in the model parameters was indicative of density-dependent habitat selection and supported a previous study showing a positive correlation between distributional area and total abundance. Density-dependent habitat selection by juvenile haddock did not generate correlations between mean length-at-age and total abundance-at-age because the proportional abundance of haddock in areas of differing growth rates remained approximately constant as total abundance-at-age increased.

Effects of condition on fecundity and total egg production of eastern Scotian Shelf haddock (Melanogrammus aeglefinus)

2003 ◽  
Vol 60 (3) ◽  
pp. 321-332 ◽  
Author(s):  
Julia L Blanchard ◽  
Kenneth T Frank ◽  
James E Simon
Keyword(s):  
Time Series ◽  
Egg Production ◽  
Significant Proportion ◽  
Melanogrammus Aeglefinus ◽  
Hepatosomatic Index ◽  
Dramatic Improvement ◽  
Scotian Shelf ◽  
Residual Variation ◽  
Condition Effect ◽  
Haddock Melanogrammus Aeglefinus

A fecundity study of the eastern Scotian Shelf haddock (Melanogrammus aeglefinus) stock during the 1997–1999 spawning seasons is reported. We developed a model that accounted for fecundity changes at the individual level and that could be used to estimate population egg production beyond the study period. Incorporating condition factors into the model (relative condition factor (Kn) and hepatosomatic index) accounted for a significant proportion of the residual variation. The model predicted that a change in Kn from 0.8 to 1.0 resulted in a twofold increase in fecundity at length. This variability was as great as that observed for fecundity–length relationships among stocks. Three time series (1979–2001) of total egg production (TEP) were constructed using different fecundity relationships: one with a condition effect, one based on length only, and one based on weight only. The magnitude of change in TEP resulting from the condition effect ranged from +30 to –20%. Condition effects during the first half of the time series resulted in an enhancement of TEP, whereas in the latter half, condition effects depressed TEP. This evaluation of TEP generated new insights into haddock stock dynamics but did not result in a dramatic improvement of the relationship between recruitment and stock reproductive potential.

Microsatellite evaluation of haddock (Melanogrammus aeglefinus) stocks in the northwest Atlantic Ocean

2001 ◽  
Vol 58 (5) ◽  
pp. 982-990 ◽  
Author(s):  
Christopher Lage ◽  
Maureen Purcell ◽  
Michael Fogarty ◽  
Irv Kornfield
Keyword(s):  
Melanogrammus Aeglefinus ◽  
Georges Bank ◽  
Effective Number ◽  
Scotian Shelf ◽  
Genetic Structuring ◽  
Northwest Atlantic ◽  
Spawning Aggregations ◽  
The Impact ◽  
Significant Genetic Divergence ◽  
Haddock Melanogrammus Aeglefinus

The goal of this study was to gain insight about the impact of intensive fishing on a single haddock (Melanogrammus aeglefinus) stock, and examine the genetic structuring of spatially discrete spawning aggregations in the northwest Atlantic. We analyzed genetic change at four microsatellite loci for Georges Bank haddock over a 40-year time span in which significant changes in demographics and abundances have occurred in the population. Allelic diversities have changed little, indicating that, although the commercial fishery has collapsed, stock sizes have remained large enough to insulate against major reductions in genetic variation due to drift. Results indicate significant genetic divergence among decadally separated samples. Potential causes for these differences include admixture from other spawning regions, fluctuations in the effective number of spawners contributing to a single spawning event, drift, or a combination of these. Examination of discrete spawning aggregations from Georges Bank, Browns Bank, the Scotian Shelf, and Nantucket Shoals indicated significant differences among stocks. Genetic distance based measures supported the clustering of Scotian Shelf, Browns Bank, and Georges Bank haddock to the exclusion of Nantucket Shoals haddock. Haddock spawning on Nantucket Shoals may be genetically discrete from other haddock populations in the northwest Atlantic.

Distribution of Early-Stage Atlantic Cod (Gadus morhua), Haddock (Melanogrammus aeglefinus), and Witch Flounder (Glyptocephalus cynoglossus) Eggs on the Scotian Shelf: A Reappraisal of Evidence on the Coupling of Cod Spawning and Plankton Production

1992 ◽  
Vol 49 (2) ◽  
pp. 238-251 ◽  
Author(s):  
Keith Brander ◽  
Peter C. F. Hurley
Keyword(s):  
Gadus Morhua ◽  
Atlantic Cod ◽  
Early Stage ◽  
Calanus Finmarchicus ◽  
Melanogrammus Aeglefinus ◽  
Scotian Shelf ◽  
Plankton Production ◽  
Peak Abundance ◽  
Haddock Melanogrammus Aeglefinus ◽  
Timing Of Spawning

In spring, Atlantic cod (Gadus morhua) spawned progressively later from southwest to northeast along the Scotian Shelf and matched the variation in peak abundance of Calanus finmarchicus. In fall, cod spawned in some, but not all, areas where Calanus were abundant. This is consistent with the hypothesis that cod spawning is coupled to copepod production, which is a part of the "match–mismatch" hypothesis proposed by D. H. Cushing. The timing of spawning was estimated from the distributions of early- and late-stage eggs of cod, haddock (Melanogrammus aeglefinus), and witch flounder (Glyptocephalus cynoglossus) collected during Scotian Shelf Ichthyoplankton Survey (SSIP) cruises in 1979–81.

Causes of Density-Dependent Catchability for Georges Bank Haddock Melanogrammus aeglefinus

1990 ◽  
Vol 47 (2) ◽  
pp. 385-394 ◽  
Author(s):  
Victor Crecco ◽  
William J. Overholtz
Keyword(s):  
Search Time ◽  
Curvilinear Relationship ◽  
Melanogrammus Aeglefinus ◽  
Georges Bank ◽  
Commercial Fishery ◽  
Commercial Catch ◽  
Stock Size ◽  
Stock Biomass ◽  
Haddock Melanogrammus Aeglefinus ◽  
Stock Abundance

We used population estimates (VPA) fishing effort and catch data for Georges Bank haddock, Melanogrammus aeglefinus, from 1964 through 1984 to test Paloheimo and Dickie's hypothesis which predicts: (1) that the catchability coefficient (q) from the commercial fishery is inversely related to haddock stock size (N) and stock area (Area); (2) that commercial catch per effort (C/f) data are curvilinearly related to stock abundance; and (3) that search time in the Georges Bank haddock fishery is inversely related to stock abundance. The catchability coefficients for the Georges Bank trawl fishery were inversely related to haddock stock size (r = −0.82, P < 0.001) and stock area (r = −0.75, P < 0.001). There was also a significant curvilinear relationship between commercial C/f and absolute and relative haddock stock biomass from 1964 through 1984. The slope estimate (B + 1) from this relationship was less than 1.0 (r = 4.18 to 8.95, P < 0.001), indicating nonlinearity between C/f and N. Finally, the relative search time expended by the haddock commercial fishery was inversely related to stock size from 1964 through 1984 (r = −0.75, P < 0.001). These results are consistent with the three predictions of the Paloheimo and Dickie hypothesis, suggesting that fishing mortality rates on Georges Bank haddock are a depensatory function of stock biomass.

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