Discriminating bluemouth, Helicolenus dactylopterus (Pisces: Sebastidae), stocks in Portuguese waters by means of otolith shape analysis

The understanding of the stock structure of a species is essential to effectively manage fisheries. Otolith shape analysis has been successfully applied in stock identification using the elliptic Fourier analysis. This method was used to assess possible differences in the otolith shape of Helicolenus dactylopterus caught around the Azores, Madeira and mainland Portugal. A total of 294 individuals ranging from 23 to 29 cm in total length, equally distributed by sex and area, were analysed. The multivariate analysis of variance performed on the otolith normalized elliptic Fourier descriptors (NEFDs) revealed significant differences for both area and sex, but no interaction was found between the two factors. In the canonical discriminant analysis an overall classification success of 69.4% and 66.7% was achieved for females and males respectively. These results suggest the usefulness of otolith shape analysis for stock differentiation of bluemouth from Portuguese waters.

Yellow perch (Perca flavescens) stock structure in Lake Michigan: an analysis using mark–recapture data

To evaluate the stock structure of yellow perch ( Perca flavescens ) in the southern basin of Lake Michigan and in Green Bay, we analyzed recaptures from a lake-wide mark–recapture study implemented from 1996 to 2001 to infer the range and pattern of movement and spawning-site fidelity. Yellow perch generally moved south along the western shoreline, west along the southern shoreline, and north along the eastern shoreline during summer and non-summer months; the magnitude of movement was greater after spawning. Spawning yellow perch frequently returned to the same site, with 35%–80% of recaptured individuals returning to their marking site. Results from multiple tagging sites within Illinois indicated that spawners may return to larger areas rather than to specific sites, suggesting that large spawning complexes exist. Despite strong fidelity in some areas, straying was evident from all sites during spawning, resulting in mixing throughout the southern basin. Such mixing could promote gene flow and diminish stock differentiation. Dispersal of yellow perch within the southern basin of Lake Michigan occurred regularly across adjacent management boundaries. Therefore, adjacent jurisdictions may wish to consider re-examining their regulations based on this information to ensure consistent, complementary regulations that incorporate the movement patterns of yellow perch.

Patterns of Larval Emergence and Their Potential Impact on Stock Differentiation in Beach Spawning Capelin (Mallotus villosus)

The environmental cues triggering larval capelin (Mallotus villosus) emergence in the St. Lawrence estuary and in coastal Newfoundland are different. In the estuary, emergence from the intertidal and subtidal spawning grounds starts with dusk and ends with dawn, indicating an active response to low light intensity. In the laboratory, emergence from undisturbed sediments collected in the field is perfectly synchronized with the dark phase of the illumination cycle. Nocturnal emergence would represent an adaptation reducing vulnerability to visual predators. Previous work has shown that in Newfoundland, capelin emergence from intertidal beaches is triggered by abrupt changes in water temperature following the sporadic advection to the coast of surface water masses characterized by low predator and high prey abundances. We argue that regional differences in the emergence pattern of the species represent different strategies to avoid predation at the onset of the planktonic drift when the vulnerable yolk sac larvae are densely aggregated. Selection acting on the behaviour of the early larval stages could contribute to stock differentiation in capelin.