Tuesday, 31 January 2017

Trends in Scottish Fish Stocks 2016

A paper on the state of gadoid (cod family) fish stocks by the University of the Highlands and islands has just been published. The paper highlights some of the significant (for the good) changes in fish stocks in recent years.

Bertie Armstrong, chief executive of the Scottish Fishermen’s Federation, said: “We are delighted this report confirms the general trend of increasing fish stocks in Scottish waters. Much of this recovery can be attributed to the innovation of our fishermen in developing more selective types of fishing gear and pioneering other initiatives such as real time area closures.

“With Brexit looming, our fishermen can look to the future with real confidence. Regaining control of our own 200-mile Exclusive Economic Zone (EEZ) will provide a sea of opportunity for the implementation of fit-for-purpose sustainable fisheries management that benefits both our fishing communities and the marine environment.

“This steady and hard-won recovery must be nurtured and continued. The report underlines the clear importance of gaining full control of our EEZ, which must be a red-line issue during the forthcoming negotiations. Access to our waters should only be considered and discussed once we have achieved this control.”

Two parameters are commonly used to reflect the state of a fish stock and the level of exploitation to which it is subject:

  • The Spawning Stock Biomass (SSB) is the estimated biomass (weight) of sexually mature fish in a stock, and is commonly used as a measure of the size of the stock.
  • The Fishing Mortality Rate (F) is a measure of the proportion of a fish stock that is removed (caught) each year. F is measured on a logarithmic scale; thus a value of 1.0 (F1.0) corresponds to 63% of the stock being removed each year, F0.7corresponds to 50% of the stock being removed and F0.5 to 39%.

Two general trends are apparent from the whitefish data:

The spawning stock biomasses (SSB) of most whitefish stocks have increased
since the mid-2000s, in some cases by substantial amounts.

The fishing mortality rates (F) for all the species covered have declined since
the mid-2000s, again by substantial amounts in some cases.

Although the sizes of some stocks (such as cod and haddock) remain below levels seen in the past, stocks of others (such as plaice and hake) are at historic highs.

Read the paper online:

The paper was published by Ian R Napier (ian.napier@uhi.ac.uk) for the University of Highlands & Islands.