Estimating and forecasting pre-fishery abundance of Atlantic salmon (Salmo salar L.) in the Northeast Atlantic for the management of mixed-stock fisheries

Abstract

Most exploitation of Atlantic salmon (Salmo salar) is restricted to “homewater fisheries”, which operate close to or within the rivers of origin of the stocks, but two “distant-water fisheries” are permitted to operate off the west coast of Greenland and in the Norwegian Sea, and take salmon from a large number of rivers over a wide geographical area. Providing robust quantitative catch advice for these mixed-stock fisheries depends upon the ability to forecast stock abundance for about 2000 salmon river-stocks around the North Atlantic, more than 1500 of which are in Europe. A “run-reconstruction” model is presented for estimating the historic pre-fishery abundance (PFA) of salmon for countries or regions around the Northeast Atlantic, based upon catch data and estimates of non-reporting rates and exploitation rates. These estimates are then used to develop predictive models of PFA on the basis of estimates of the egg deposition, derived from the run-reconstruction model and various environmental data. Although the selected environmental indices correlated with the PFA of both southern and northern European stock complexes, the main statistical significance in the forecast models was provided by temporal trends in the PFA. Clearly, such a model is only tenable in the short term, and will be poor at predicting a major change in stock status. Alternative approaches, based upon juvenile production indices and including Bayesian techniques, are therefore being considered.

Links between patterns of marine growth and survival of Atlantic salmon Salmo salar, L.

“…data). This is an estimate of the number of fish available before exploitation starts, backcalculated from the catches, and estimates of the rates of exploitation, natural mortality and unreported catches (Potter et al , 2004; E. C. E. Potter, L. P. Hansen, G. Gudbergsson, W. Crozier, J. ErKinaro, C. Insulander, J. MacLean, N. Ó Maoileidigh & S. Prusov, unpubl. data).…”

Static versus dynamic model for forecasting salmon pre-fishery abundance of the River Bush: a Bayesian comparison

“…For a fuller accounting of uncertainty, the PFA forecast should be obtained after an integration over the measurement error associated to the PFA estimation. The elaboration of a single and consistent probability model from the current ad hoc PFA estimation procedures (Potter and Dunkley, 1993;Rago et al, 1993;Kennedy, 1994, 2002;Potter et al, 1998) is not completed as yet (see Potter et al, 2004 for a review of progress). It is most needed in a management advice perspective.…”

A general model for reconstructing salmon runs

“…It is known that there are other sources of mortality: for some populations, natural mortality may be substantial, especially where the migration is arduous or when environmental conditions are unfavorable (Cooke et al 2004(Cooke et al , 2006Crossin et al 2007); additionally, fishing gear may scar escaping fish, causing delayed mortality (Baker and Schindler 2009). Other run reconstruction models have included natural mortality (Potter et al 2004;Quinn and Gates 1997), and it would be relatively easy to include natural mortality in SYRAH using the equations in Branch (2009).…”

“…Backward run reconstruction models start with the daily escapement counts (or a distribution fit to them) and move fish back in time and space, adding catches as appropriate (Potter et al 2004; Starr and Hilborn 1988;Templin et al 1996). Backward models can be calculated easily provided that salmon headed for a particular river system have a single migration pathway and deterministic migration or pooling times.…”