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Hake population has withstood overfishing, thanks to the warming of the sea

24.08.2011
Hake is constantly fished in the waters of the European Atlantic Ocean and, nevertheless, resists stock depletion relatively well. At times nature is capable of correcting the mistakes made by humans.

Ms Nerea Goikoetxea, a researcher at Azti-Tecnalia, has been witness to this. She has investigated the population dynamics of the northern European hake population, observing which environment has favoured the species since the 90s to date: the sea has turned milder, and so larvae have grown better and faster.

So, despite the biomass being less due to fishing, the rate of survival of the larvae has been enhanced, as well as opening up to future generations. Ms Goikoetxea presented her thesis at the University of the Basque Country (UPV/EHU) with the title: Influence of the northeastern Atlantic oceano-meteorological variability on the northern hake (Merluccius merluccius). Analysis of the 1978-2006 period.

As Ms Goikoetxea bore out in her study, the factors related to the population density (fishing and its impact on the stock of hake at the age of fecundity) are obviously important in understanding the evolution of the species. But, equally important as this may be other matters which have nothing to do with density, such as environmental conditions. As is explained in the thesis, what happened after the 90s is a good example of this.

Low biomass, rise in success of recruitment

Ms Goikoetxea has shown that, especially between 1895 and 1990, the adult population of hake (SSB or spawning stock biomass) dropped considerably, probably because of overfishing. If only this factor is taken into account, it would be logical to think that the generational turnover of hake runs a risk every year, but this has not been the case. Although the SSB and the total recruitment (the amount of young hake that survive to the age of fecundity) fell from the 1990`s, the success of recruitment increased. In other words, proportionally speaking, more eggs laid by these generations have survived long enough to become adult hakes. The researcher points to nature: until the 90s, fishing harmed the hake population but, since then, favourable conditions have arisen which have had a greater impact than the negative consequences derived from fishing.

Concretely, Ms Goikoetxea explained that there was a change in the ecological regime on the continental platform in the north-eastern Atlantic Ocean zone, which warmed the waters that are host to the hake of northern Europe. The warming occurred between the end of the 80s and the mid-90s. On the one hand, the phenomenon known as the North Atlantic Oscillation or NAO positive index occurred: low pressures in the area of Iceland dropped notably, as did high pressures in the Azores. Simultaneously, the Gulf Stream grew stronger. All this increased the transport of warm water towards the north east. All this warming and the rise in success of recruitment occurred simultaneously.

The warmer the waters, the faster the egg-laying

Goikoetxea concluded, thus, that warm temperatures can be beneficial for hake, especially in the early stages of their life cycle. On there being a rise in the temperature of the water, the period and space for laying eggs are extended, and so the numbers of surviving individuals are greater. Likewise, as the larvae grow faster in warmer waters, their period of vulnerability is shortened, and it is more feasible to survive. Also, the transport of water in a north-east direction eases and facilitates the route from egg-laying zones to breeding grounds, the hake thus growing in the most appropriate locations for each stage. Therefore, the success of recruitment rises.

In consequence, while reiterating that the quantity of the adult hake population (conditioned by fish catches) may have great bearing on generational turnover, the environmental impact should also be taken into account. Amongst these environmental factors, Ms Goikoetxea makes reference to wind transport, to anomalies in the temperature of the northern hemisphere and to the amount of food available during egg-laying.

About the author

Ms Nerea Goikoetxea Bilbao (Bermeo, 1980) is a Biology graduate and has just finished a European Master’s degree in Marine Environment and Resources. She drew up her thesis under the direction of Mr Xabier Irigoien, coordinator of the Departments of Oceanography, Biology and Ecosystems and Management of Pelagic Resources at Azti-Tecnalia. She defended her PhD at the Department of Zoology and Animal Cell Biology of the Faculty of Science and Technology at the UPV/EHU. Ms Goikoetxea undertook her thesis at Azti-Tecnalia and is currently a researcher there.

Amaia Portugal | EurekAlert!
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http://www.elhuyar.com

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