Lawrence J. Buckley

Vertical distribution of cod and haddock eggs and larvae, feeding and condition in stratified and mixed waters on southern Georges Bank, May 1992

Abstract In late May 1992, cod and haddock eggs and larvae were sampled at discrete depths using MOCNESS on the southern flank of Georges Bank when seasonal stratification of the water column was developing. A deeper, stratified site (80-m bottom) was sampled over 7 days in relation to the temporal evolution of vertical structure and compared to a nearby shoal, mixed site (50 m). Sampling also was conducted to the west along two transects in the Great South Channel. Larval biochemical composition was measured and nutritional condition inferred from RNA:DNA ratios. During the period 22–24 May 1992, surface warming resulted in a temperature gradient from 6 to 10°C (0.6 δt units) in the upper 20 m at the stratified site. Gadid eggs (93% haddock) were most abundant (6–14 per 100 m3, on average) in the surface 20 m, with maximum density just above the base of the thermocline at 20-10 m. The few recently-hatched larvae (5–6 mm) caught were broadly distributed in the water column, with maximum average densities (1–3 per 100 m3) deeper at 10–40 m. The naupliar and copepodite stages of Pseudocalanus spp. were principal prey of these larvae, and also were more abundant (3–7 prey 1−1) in the surface 20 m, with a maximum density at 20-10 m. A moderate storm on 25 May mixed the upper part of the water column to 5–6°C. The day after the storm, gadid eggs and copepods had highest densities in the surface 10 m. At the shoal (mixed site) egg densities were low (1–3 per 100 m3) and distributed evenly through the water column. Cod and haddock larvae were larger (7–8 mm modal length) and more abundant than at the stratified site. At night, they were evenly distributed at 4–6 per 100 m3 on average, but by day, maximum density increased to 6–16 per 100 m3 in the deepest strata sampled (40–30 m). The larger larvae at this site preyed predominantly on copepodite stages of Pseudocalanus spp., which were uniformly distributed in the water column. Of all the larvae sampled for biochemical analysis, 10% of haddock and 1.5% of cod had ratios below 4.1. Based on laboratory studies, fish larvae with RNA:DNA ratios below 4.1 are considered to have been in poor condition. There were no larvae in poor condition at the Great South Channel Transect, where their mean size was greatest; no larvae were collected at the stratified site for comparison. At the mixed site, cod larvae sampled before and after the storm had identical ratios, while haddock larvae had significantly higher ratios after the storm. Larvae from different sampling depths had significantly different ratios, inferring that they remained together long enough to acquire a unique signature.

Does the fall phytoplankton bloom control recruitment of Georges Bank haddock, Melanogrammus aeglefinus, through parental condition?

In 2003, the Georges Bank stock of haddock (Melanogrammus aeglefinus) experienced the largest recruitment event recorded during its assessed history. Several hypotheses have been advanced to explain recruitment variability in this much-scrutinized stock, including variability in the retention of eggs and larvae on Georges Bank, the timing of haddock spawning, and variability in the spring bloom, which influences larval growth and survival. Although these processes may contribute to the formation of successful year classes, none of the factors associated with these previous hypotheses provides an adequate explanation of the 2003 recruitment event. We analyzed data on the dynamics of the fall phytoplankton bloom the year prior to spawning and show it to be highly correlated with subsequent recruitment. We suggest that the fall bloom affects recruitment through enhanced condition of adults and by increasing the quantity and quality of their reproductive output, which in turn leads to a higher probability of ...

Heterogeneity of paralytic shellfish poisons. three new toxins from cultured Gony aulax tamarensis cells, Mya arenaria and Saxidomus giganteus

1. 1. Three new toxins (gonyautoxin-IV, gonyautoxin-V, and neosaxitoxin) have been isolated from cultured Gonyaulax tamarensis cells bringing the total number of paralytic shellfish poisons to seven. 2. 2. Soft shell clams Mya arenaria, exposed to a bloom of G. tamarensis, have been found to contain gonyautoxin-IV and neosaxitoxin in different proportions to those found in the dinoflagellate. 3. 3. Neosaxitoxin has been also isolated from Alaska butter clams, Saxidomus giganteus. This is the first report of the presence of a toxin other than saxitoxin in Alaska butter clams.

Reply to the comment by Payne et al. on “Does the fall phytoplankton bloom control recruitment of Georges Bank haddock, Melanogrammus aeglefinus, through parental condition?”Appears in Can. J. Fish. Aquat. Sci. 65: 1076–1086.

Payne et al. (Can. J. Fish. Aquat. Sci. 66: 869–872, 2009) raised several points concerning the handling and interpretation of data that went into an analysis of the population dynamics of Georges Bank haddock that suggested a relationship between the fall phytoplankton bloom and recruitment (Can. J. Fish. Aquat. Sci. 65: 1076–1086, 2008). Their main points were the manner in which logarithmic transforms were applied, whether the 2003 year class was truly as large as estimated in a 2006 assessment, and if correlation analyses of zooplankton data should be reconsidered. The reply to these comments was aided by a new assessment which provided additional years of data and improved the quality of the recruitment time series. The reply analyses showed that the relationships were robust to the way the logarithmic transform was applied, the initial estimates of the size of the 2003 year class were correct, and relationships between recruitment and spring zooplankton biomass levels remain statistically insignific...