NASCO Workshop for North Atlantic Salmon At-Sea Mortality

Reductions in marine survival have been implicated as the primary reason for the North Atlantic pattern of declines in Atlantic salmon abundance over the past five decades. With the goal to improve the scientific assessments and advice for the conservation of wild Atlantic salmon (Salmo salar L.) in the North Atlantic, ICES in consultation with the North Atlantic Salmon Con-servation Organisation (NASCO) convened a series of workshops to explore how best to inte-grate available data on salmon for use in models to advance the conservation of wild salmon at sea. The first workshop (WKSalmon) was held 24–28 June 2019 for the purpose of identifying data sources that could inform estimates of at-sea salmon mortality as well as ecosystem data including oceanographic time-series, plankton surveys, pelagic or demersal fish surveys that describe the marine ecosystem occupied by Atlantic salmon.

Atlantic salmon populations are broadly distributed in the western and eastern continental areas of the North Atlantic (42 to 68°N). There are extensive population-specific data on life-history traits including growth rates, maturation, marine survival and fisheries exploitation across the distributional range of the species. Reconstructions of abundance extending five decades are available for regional groups of populations. Atlantic salmon is a pelagic marine species, and groups of populations from the North Atlantic utilize common feeding areas at key points of the marine phase. The absence of synoptic and systematic marine surveys for Atlantic salmon preclude a full understanding of its distribution and population dynamics at sea.

Knowledge of marine ecosystem components relevant to Atlantic salmon including physical and biological oceanography, prey, competing species, and potential predators is extensive although the temporal (seasonal, annual) and spatial scales of coverage of these data is highly variable and does not overlap with the entire anadromous phase of salmon. The physical oceangraphic fea-tures monitored by remote sensing including sea surface temperature and indices of primary production have the highest spatial resolution, and the broadest domain coverage that encom-passes the entire North Atlantic and months when salmon are at sea. The indices of secondary production have a broad spatial and temporal coverage, but a lower resolution compared to re-mote sensing indices. The pelagic fish community is sparsely sampled, with the best coverage in the Northeast Atlantic for May, and July–August and no current coverage in the Northwest Atlantic.

The options for testable hypotheses are constrained by the availability and representativeness of monitoring data for the components of the marine ecosystem occupied by Atlantic salmon. Few of the datasets described, in particular for Atlantic salmon, are readily available as open data or from websites. The most readily available data are for climate indices and physical oceano-graphic features. The large amount of ecosystem information is compiled and maintained within a diverse community of scientific experts with to date limited cross-fertilization and networked analyses. The time scales and spatial scales of observations are variable, of differing complexity requiring a range of analytical skill sets, but seemingly extractable with some concerted effort.