CATCH-AND-RE­LEASE IM­PACTS ON A FISH­ERIES GE­NETIC HEALTH

NZ Fish & Game - - Letters - David moate

EN­JOYED THE THOUGHT-PRO­VOK­ING AR­TI­CLE in Is­sue 88 about the last­ing ge­netic im­pli­ca­tions of catch-and-re­lease in headwater fish­eries ( An Eye

To­wards The Fu­ture) and agrees with the sen­ti­ment that catch-and-re­lease is an im­por­tant part of the fish­ing scene in New Zealand, but not nec­es­sar­ily for the rea­sons dis­cussed.

Species ge­net­ics are de­vel­oped over a long time and are slow to change, but char­ac­ter­is­tics change more quickly as they are con­stantly in­flu­enced by their habi­tat, food, and pre­da­tion. This ex­plains why, for ex­am­ple, brown trout that travel into the sea can reach huge sizes while high al­ti­tude, land­locked lake pop­u­la­tions can be stunted, but are still ge­net­i­cally the same. Sub-species, or even new species, are formed when one of these pop­u­la­tions de­velop char­ac­tis­tics best suited to that en­vi­ron­ment, but are iso­lated for many mil­lions of years. Our long fin eel is a good ex­am­ple of a new species of eel af­ter be­ing iso­lated from other eel pop­u­la­tions for more than 80 mil­lion years.

Trout are a very ver­sa­tile species that have been moved all around the world, cre­at­ing many new fish­eries, each with its point of dif­fer­ence. But a brown trout is still a BT and rain­bow is still a rain­bow even when lo­cal con­di­tions have started to cre­ate ob­served dif­fer­ences. Add to this the fact that in­di­vid­ual trout can vary in length, colour, and con­di­tion in re­sponse to food sup­plies and habi­tat con­di­tions. For ex­am­ple, that typ­i­cal 4lb fish you see in your lo­cal wa­ters could be 3lb af­ter a dam­ag­ing flood and 8lb dur­ing a mice plague. Age varies as well, with a 4lb trout caught in the Mataura catch­ment aged at 13 years and 32lb caught in the Wa­iau River aged at four years. Pro­vide lots of food and trout will grow big quickly -- that is why they are farmed.

In terms of trout ge­net­ics in headwater fish­eries, let us not for­get that New Zealand re­search has con­firmed that these large trout did not ac­tu­ally grow large in these wa­ters. They grew in the lower sec­tions of the rivers or lakes and then mi­grated up­stream to breed. Some stay -- mostly males -- to breed again next year and can main­tain their size by se­lect­ing the larger macroin­ver­te­brates easily spot­ted in the clear wa­ter. So this ex­plains their pres­ence, but does not sup­port an iso­lated ge­netic pool of large fish in the head­wa­ters. In­stead, it shows how im­por­tant it is for trout to have full ac­cess to a catch­ment to sur­vive all its vari­ables and take ad­van­tage of op­por­tu­ni­ties to grow and re­pro­duce. Growth for fish, in­clud­ing trout, equates to more pro­duc­tive breed­ing and sur­vival from preda­tors.

Based on this knowl­edge, fish­ery man­agers spend a lot of an­glers’ li­cence fees on de­fend­ing wa­ter­ways from dams and pol­lu­tion to re­tain fish pas­sage and habi­tat through­out a catch­ment, not just the head­wa­ters. Re­search into headwater fish­eries use has con­firmed that the pres­ence of large trout is the key value sought by an­glers, so catch-and-re­lease ar­eas were tri­aled and found to have lit­tle in­flu­ence on trout size and num­bers so low bag lim­its and slot sizes lim­its were in­tro­duced to mainly pro­tect the fish­ing ex­pe­ri­ence for an­glers rather than a pop­u­la­tion pro­tec­tion mea­sure. Catch-and-re­lease has been fre­quently vol­un­tar­ily prac­ticed in head­wa­ters for many decades now and it is prov­ing to be ef­fec­tive at re­tain­ing larger trout to the in­creased num­bers of an­glers ac­cess­ing these ar­eas, but will catch-and-re­lease in­flu­ence ge­net­ics in the fu­ture?

Given trout come from a very ver­sa­tile ge­netic pool, which is con­stantly mixed by new ar­rivals from the catch­ment ( browns even from other catch­ments) and con­tin­ues to be shaped by en­vi­ron­men­tal con­di­tions, I think that given these fish rep­re­sent only a tiny por­tion of a fish­ery it is un­likely catch-and-re­lease in­flu­ences ge­net­ics. Per­haps the op­po­site is true, as catch-and-re­lease al­lows these trout to con­tinue to breed, lim­it­ing new ar­rivals that may bring with them im­proved lo­cal char­ac­ter­is­tics that will even­tu­ally lead to a fish bet­ter adapted to that en­vi­ron­ment.

My point of view is that vol­un­tary catch-and-re­lease is an im­por­tant fish­ery man­age­ment prac­tice that helps to re­tain larger trout, which can be caught by in­creas­ing num­bers of headwater an­glers. But if we want to pro­tect the ge­net­ics of a fish­ery, we must pro­tect its whole en­vi­ron­ment from habi­tat dam­age and dams to al­low the con­tin­u­ing de­vel­op­ment of lo­cal char­ac­ter­is­tics that will ul­ti­mately dic­tate the fish­eries fu­ture.

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