The North Atlantic Marine Mammal Commission


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North Atlantic Stocks

Stock Definition

Morphometrics (body size and shape) and genetic studies point to the existence of several stocks of fin whales in the North Atlantic (Daníelsdóttir et al. 1991, 1992, Jover 1991, Bérubé et al. 1998). In addition, fin whales can be differentiated into regional groups by the sounds they make (Hatch and Clark 2004). However, at present, breeding grounds have not been identified for fin whales within the North Atlantic and there is not enough information to place boundaries around fin whale stocks with certainty.

Feeding areas as management units

For management purposes, fin whale stocks have therefore been generally defined, based primarily on the summer feeding concentrations of whales. Fin whales appear to return to the same feeding grounds year after year, and tagging studies have shown little relocation of whales outside of the summering stock areas in which they were tagged (IWC 1992).

Current management is based on stock boundaries proposed by the International Whaling Commission in 1977, based on the best available evidence at that time (Donovan 1991). Since then new evidence has not been contrary to the original stock delineation, but has allowed a refinement of the stock definition (IWC 2008, NAMMCO 2008).

The baseline stock hypothesis distinguishes

  • 7 feeding/management areas (Figure below, upper: Canada; West Greenland; East Greenland; West Iceland; East Iceland - Faroes; North - West Norway; Spain.

  • 4 breeding populations (Figure below, lowest): West, Central, East and Spain.

  • Central population split into 3 sub-populations linked by diffusive mixing (Figure below, lowest):C1, C2 and C3.

Alternative hypotheses consider two forms of variation about the baseline hypothesis:

a) different mixing of breeding stocks on the feeding grounds.
b) a simplification of the baseline hypothesis by reducing the number of breeding populations from 4 to 3-2.

All of these hypotheses are used in simulation testing of various management regimes to ensure that projected levels of harvest will not be harmful to any stock. This stock definition may not fully describe the stock structure of fin whales in the North Atlantic, but reconciles best the available information from genetic and non-genetic evidence, and is considered safe for management purposes.


IWC NEW management areas


Fin whale stocks as recognised by the IWC and NAMMCO (IWC 2007b, NAMMCO 2007b).


Basic stock structure IWC