Alaska hatchery salmon responsible for killing PWS herring? (June 2011)

Alaska hatchery salmon responsible for killing Prince William Sound herring? No (more) red herring!

Editorial by Bertrand Charron first published on 30.06.2011

A study published last month (see: http://is.gd/s338tH) to update previous reviews of the 1993 stock decline of Pacific herring in Prince William Sound, Alaska, highlights analysis which indicate that ”the population dynamics of the sound’s herring are influenced by oceanic factors, nutrition, and, most substantially, hatchery releases of juvenile pink salmon”. The study puts in perspective the impact and the “sustainability” issues surrounding Alaska’s so-called ‘wild’ salmon fisheries (about 30% of the 2011 total ‘wild’ [and marketed as.] salmon harvest will be made of ‘ranched salmon’). We make this point as there is a perception that (MSC eco-labelled) Alaska salmon are all (truly) ‘wild’.

Alas… since many decades, Alaska’s commercial salmon fishing industry has heavily relied upon hatchery outputs to generate some of its harvestable stocks; whilst at the same time often being extremely critical (in itself, not a ‘crime’…) of farmed salmon. However, the North American public – and some of the aquaculture critics – would benefit in knowing/acknowledging that use of hatchery fish can & does also have environmental impacts. I.e. that the very ‘sustainability’ arguments oft branded against fish farmers can (and should) also be used to scrutinise the (environmental, economic, ‘ethical’…) sustainability of AK’s ‘enhanced’, ‘not truly wild’ salmon fisheries. Only when it will be accepted that much of AK salmon industry’s ‘viability’ depends on the very aquaculture technology it decries will the debate (re. the ‘sustainability’ of ranched & farmed salmon) be allowed to leap forward…

Even the United Nation’s FAO (but not the MSC…) recommends that ‘enhanced’ and ‘truly wild’ fisheries be distinguished and accordingly labelled in the marketplace. This means going beyond politics, lobbying, marketing, commercial interests and ill-communication. Any takers?!

The scientists add that “pink salmon fry releases have increased to about 600 million annually and may disrupt feeding in young herring, which require adequate nutrition for growth and overwintering survival.”

In their conclusion, the scientists says they have: “assessed the evidence for and against the principal decline and poor recovery hypotheses and find no evidence that oil exposure from the Exxon Valdez oil spill, harvest effects, spawning habitat loss, the spawn-on-kelp fishery, or disease have led to either the decline or poor recovery of PWS herring. Our re-examination of available information and recent modeling outcomes supports earlier conclusions (Pearson et al. 1999) that poor nutrition is the probable cause of the 1993 decline.

[…] The evidence supports the contention that disease during the decline was a secondary response after a portion of the PWS herring population was stressed by poor nutrition.

Poor recovery probably results from several factors. Since 1993, no strong year classes have emerged in the GOA herring populations, including that at PWS. This lack of strong year classes appears to derive from regional-scale ocean environmental factors.

“Beyond the regional-scale factors, two other factors specific to PWS appear to be reducing herring biomass and recruitment. First, predation by an increasing number of overwintering humpback whales may prove to be removing a substantial proportion of the adult herring in PWS. Second, interactions with juvenile pink salmon released from PWS hatcheries may be influencing nutrition in juvenile herring and their subsequent growth, survival, and recruitment. “

[…]

Reference: Hypotheses concerning the decline and poor recovery of Pacific herring in Prince William Sound, Alaska. Rev Fish Biol Fisheries DOI 10.1007/s11160-011-9225-7

http://www.springerlink.com/content/l20181700145wk5x/fulltext.pdf

Read also: Are hatchery salmon killing off herring in Prince William Sound? Anchorage Daily News (29.06.2011).

 

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