Of 5074 adult American shad, Alosa spidissima, tagged in the Annapolis River, Nova Scotia, during the 1981 and 1982 spawning runs, 292 (5.8%) were recaptured, 180 in the river during the same year, 56 in the river in subsequent years, 53 at distant marine sites, and 1 in another Nova Scotia river. Recovery from 6124 adult shad tagged in a marine environment (Cumberland Basin, Bay of Fundy) was similar (395 recaptures, 6.5%) but distribution was markedly different. Thirty-five were taken in the Basin during the same year, but only 7 in subsequent years. Conversely, 139 were recaptured at distant marine sites, and 214 in rivers from the St. Lawrence River, Quebec, to the St. John's River, Florida. Assuming equal probabilities for recapture within this species' geographical range, Annapolis River freshwater recaptures were specific for the Annapolis River but Cumberland freshwater recaptures were nonspecific. Except for two returns, possible strays, fidelity to the Annapolis was 97%.

This paper reviews the current knowledge on the ecology of widely distributed pelagic fish stocks in the North Atlantic basin with emphasis on their role in the food web and the factors determining their relationship with the environment. We consider herring (Clupea harengus), mackerel (Scomber scombrus), capelin (Mallotus villosus), blue whiting (Micromesistius poutassou), and horse mackerel (Trachurus trachurus), which have distributions extending beyond the continental shelf and predominantly occur on both sides of the North Atlantic. We also include albacore (Thunnus alalunga), bluefin tuna (Thunnus thynnus), swordfish (Xiphias gladius), and blue marlin (Makaira nigricans), which, by contrast, show large-scale migrations at the basin scale. We focus on the links between life history processes and the environment, horizontal and vertical distribution, spatial structure and trophic role. Many of these species carry out extensive migrations from spawning grounds to nursery and feeding areas. Large oceanographic features such as the North Atlantic subpolar gyre play an important role in determining spatial distributions and driving variations in stock size. Given the large biomasses of especially the smaller species considered here, these stocks can exert significant top-down pressures on the food web and are important in supporting higher trophic levels. The review reveals commonalities and differences between the ecology of widely Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site Highlights ► Comparative review of current knowledge on the ecology of widely distributed pelagic fish stocks in the North Atlantic basin. ► Emphasis on food web role and factors determining spatio-temporal distributions and changes. ► Overview of modelling approaches.

No abstract

Melvin, G. D., Stephenson, R. L., and Power, M. J. 2009. Oscillating reproductive strategies of herring in the western Atlantic in response to changing environmental conditions. – ICES Journal of Marine Science, 66: 1784–1792. Herring are broadly distributed in the western Atlantic, but reproductive activity is restricted to the central portion, from Cape Cod to northern Newfoundland. Spawning extends from early spring to late autumn. Two spawning types are recognized: spring spawners and autumn spawners. At the southern extreme, spawning occurs almost exclusively in autumn, whereas in the north, spring spawners prevail. Mid-range, both strategies are common, with spawning occurring throughout the entire season. We postulate that the temporal intra-stock dominance of spawning type is an adaptive reproductive strategy to changing environmental conditions. A conceptual model is presented to describe how reproductive success can oscillate between spawning strategies. In most years, environmental conditions appear to favour one type or the other, although strong year classes can co-occur when conditions are right. The recent change in environmental conditions, characterized by a general warming trend, favours autumn spawners and is consistent with our model. At the distributional extremes, stocks are restricted to a single spawning strategy, and broad-scale environmental changes can introduce large interannual variability and limit the reproductive and recovery potential of a stock. The dependence of a stock on a single spawning season may result in longer times to recover to target levels.

American shad (Alosa sapidissima) concentrate each summer in the basins of the inner Bay of Fundy during their coastal migration. Tag returns from 6124 marked shad indicated that these fish return to every important shad spawning stream on the Atlantic coast. Ten meristic and 16 morphometric characters of shad collected from 14 rivers (range: Florida to Quebec) were used to develop linear discriminant functions (LDF). Variables which differed significantly (p < 0.05) between the sexes, year of sampling, and the time of collection during the spawning run were removed prior to LDF classification. The highest mean percent correct classification was achieved by the allocation of fish into regional groups, after classification into individual rivers, using pooled meristic and morphometric variables: 87.2% for males and 82.4% for females. The functions were then used to assign shad from a mixed populations (Cumberland Basin) to individual rivers and regions. Of these, 10.9% were assigned to rivers south of Cape Lookout, North Carolina, 38.1% to rivers between Cape Lookout and Cape Cod, 32.5% into rivers of the Bay of Fundy, and 18.5% into rivers in the Gulf of St. Lawrence. In-river tag returns were compared with LDF classification and were found to be similar.