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Bass Dynamics

Aug 01,2008 SACN

BC: Yes the stock biomass is larger that say in the 80's , then we had a pound of butter spread over an area that stretched from the Wash , along the Channel and up to Anglesey.

Now we have  two pounds of butter but it is now spread all around the UK coast , the Dutch and Danish coast and all the way to Norway , the spread is now so thin that the numbers of fish per mile ,i.e. the stock density , is to low for the needs of RSA.


Bassman: Is it not the case that the increased biomass of bass as stated is made up of larger numbers of smaller fish as opposed to previously when we had lower numbers of larger fish BUT the numbers of larger fish then were more numerous than they are now.

It is perfectly possible that before pair trawling found the aggregations of larger pre-spawning and spawning females and before the onset of heavy inshore gill netting,  there was a spawning stock biomass of larger fish which included enough larger specimens to ensure that anglers encountered them on an increased frequency by comparison to now.

The surplus of fry produced by these females each year over and above those required to ensure repopulation, either died as the available habitat niches in estuaries were fully occupied or were mopped up in the larval and fry stages by predators or did not survive the colder winters.

As gill netting was in its infancy for bass, enough escaped from the estuaries to maintain the status quo, a sort of natural equilibrium.

What we have now is far less in the way of bigger mature bass, leaving only just enough bigger fish to keep the estuaries topped up each year with fry (no surplus to buffer poor years) plus a migration of those fish approaching 36cm into other estuaries due to increasing temperatures and favorable climate which increases juvenile survival.

When the winters were colder the juvenile bass stayed in the southern and welsh estuaries they did not migrate.

This warmer water migration results in a greater distribution of smaller fish over a wider area (thinly spread butter to quote Bob) and greater juvenile survival giving the appearance of increasing numbers.

That is why anglers find no shortage of small bass in a larger number of estuaries but very few big ones.

The additional pressure on the larger fish over and above the pair trawlers is the increased number and soak times for gill nets which take a very high number of the immature bass leaving the minimum to grow on a become mature and repopulate if they escape the pair trawlers.

There will come a point soon if commercial exploitation continues unchecked when the break point is reached.

This is when the number of larger spawning females drops below the level which can produce enough eggs to occupy the available estuary niches.

Continued gill netting pressure on the recruitment fishery (fish leaving the estuaries at 36cm) reduces escape to become mature and eventually the number of smaller bass will also start to decline as they are not replaced despite favorable environmental conditions.

If we get a double whammy of partly fry filled estuaries (not maximized with all the bass fry an estuary can hold due to reduced numbers of large females and therefore eggs) plus a couple of hard winters there will be very poor survival of the fry and big holes in the year classes for years to come.

I believe John L has already started seeing low numbers of  0 and 1 bass since 2003 in his estuary surveys and we have not had very harsh winters.

There can only be one reason for this and that is that the mature female spawning has been poor or there are now too few mature female fish to produce enough fry to fully occupy the estuary niches.

The oft quoted comment about bass being fished sustainably by ICES is always misunderstood.

What this quote means is that there are enough 36cm bass around to enable commercials to continue to crop them each year and make a living without there being a significant decline in the smaller fish being available to commercials as seen in catch versus effort calculations.

The commercial catches or weight of bass caught each year however can be achieved either as previously with less numbers of bigger fish or as now, with higher numbers of smaller fish ��" the end of year tonnage is the same.

In this sense this ‘fished sustainably’ term is about commercial sustainability only.

Recreational sustainability is very different as it requires a more natural distribution of length classes of bass including good numbers of fish between 5-10lb .

This is why BASS want more and bigger bass.

We want Recreational sustainability not commercial sustainability.


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