Dumb question.

I'm hoping that somebody more familiar with commercial fishing methods than myself could provide some insight on the effectiveness of "minimum mesh size" requirements in creating semi-selective gill net fisheries.

I've gathered from a bit of research that minimum mesh size is typically defined by the "stretch measure" which counts the number of vertical inches (or cm) between each knot. 6" minimum mesh size seems pretty common in these parts. I assume in this case that juvenilles get through, jacks get through, bulls and cutthroat get through, etc., while fish around 4-5" deep are retained. I feel like I've seen a lot of fish in this size range over the years with some abrasion around the dorsal/midsection, and a few bigger fish with more extensive trauma. After a conversation with a biologist this week, though, I'm wondering (based on his claim) if there is an upper size limit for effectiveness as well (a slot limit enforced by the net, if you will).

I gather that once a fish is in past the gillplate, it's retained unless it can fit through the hole or gets lucky. Is that accurate? If so, I figure the only other fish that get "past" a net must be fish deeper than 4-5" (but probably more like 6-7") at the gillplate (fish that don't fit into the holes in the first place and swim around in circles until they find their way upriver). I've never taken a girth measurement at the gillplate on any fish, but it seems this would be a very large fish (especially if it was a steelhead), such that the "range" this biologist spoke of is mostly imaginary, particularly in fisheries where very large fish are rare.

Can anybody comment on this?

Thanks,
-IS

Yeah.. About as selective as me getting to pick our President......

Keith

...and obviously Hillary didn't make it!

(Sorry Keith...couldn't stop myself)

6 inch mesh = 12 inches of girth.

That means any fish with a girth smaller than 12' can either swim or wriggle thru (with obvious net marks) thru the curtain. For any fish larger than a 12" girth, it's a death sentence.

So yes, gill nets are selective.... they selectively maim and/or KILL anything bigger than the chosen mesh size.

And GDITMMM!

Thats pretty messed up I'd like to gillnet a couple of indians!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Before answering the question, one needs to frome the question clearly.

Gillnets are very selective. The target a size of fish. This was clearly shown in the Shagit in the 1980s. Because of concerns for coho, the in-river fishewry for chum was consuted with 6 or 6.5 inch minimum sytretcg mesh. Lots of chum and very few coho, were caught. On December 1, when management changed to steelhead and minimum mesh dropped to something like 5", coho showed up in the catch.

They select for size, not for species. As such, fishing for sockeye comes with a maximum, in order to reduce catch of larger Chinook. The selectivity is also controlled by how the net is hung.

As fished now, gillnets in a river are way more selctive for the stocks that can sustain harvest than any hook and line (sport or commercial troll) operating in the ocean. They are probably more selctive than purse seines, espceially whn you dump 500-1000 fish on the deck and try and sort through for the non-target species.

Ickstream Steel,

Gillnets are the most selective common commercial fishing gear this side of fish traps. As Carcassman mentions, gillnets are selective for fish size, and as FNP points out, 6" of stretched mesh = 12" of girth that is being fished for. Gillnets select for the narrowest size range of fish among species with a fusiform (torpedo) like shape, such as salmon and steelhead. A gillnet of a given mesh size will catch a wider size range of fish like the rockfish species, although gillnetting for those species is generally impractical.

Salmonids that are significantly smaller - juveniles, jacks, or under-sized adults - and significantly larger are typically excluded from a given gillnet. Monofiliment gillnets are more size restrictive than multi-strand (Seven-strand, Miraclestrand) nets that stretch more than mono. Hanging a gillnet also affects its selectivity. Hung "even" in the conventional diamond-shaped openings is more size selective than a net that is hung slack. Slack hung multi-strand nets are the choice for making the so-called tangle nets in the lower Columbia sorta' selective spring chinook gillnet fishery. A slack hung multi-strand net in a small size that cannot gill a chinook will tangle chinook of various sizes in the teeth and external mouth parts. A fair amount drop out of the net, but most are tangled well enough to be landed. The flaws with tangle nets in that fishery is that the nets tangle chinook, allowing them to be sampled for adipose fin presence is that the fish are extremely sensitive to net handling in tide water, so a significant number of unmarked fish die anyway, and the tangle nets are perfect for gilling and killing steelhead present in the river at the same time.

So yes, gillnets are selective for size, but they are not selective between marked and unmarked, hatchery and wild fish.

Sg

Gillnet can also be considered a selective harvest method when they are used in the off channel select net pen SAFE areas, such as those found along the lower CR.

Thanks for the replies (and pictures).

So according to Sg there is an upper size limit for which a gill net is effective, consistent with what I was told (by a different biologist). It would make sense those few larger fish I've encountered that appeared to be net-marked were fish too large to fit into the mesh past the gill plate (especially if mesh size had been dropped to 5" for winter steelhead-targeted fisheries). A maimed fish is more likely to spawn than a dead fish, but I would be interested to see how much difficulty a fish "too large" has in navigating past a series of interleaved nets, and what sort of consequences would be expected for survival/fitness, especially if there was a holdover period involved (e.g., spring chinook, sockeye, summer steelhead).

I haven't taken many measurements on fish, but I'm imagining 12" girth equates to 5 lbs. or so - so fish from 13" at the dorsal on up to 13" at the gillplate (with a "fusiform" body, maybe 18-20" at the dorsal?) would seem caught one way or another. Thus the expected composition of fish upstream of the net is lots of 4-6 lbers, with a few 18-22 or more; or in a population that never had 18-22s, just the 4-6 lbers. Semi-accurate?

Time to go think about something else.

-IS

Evidently WDFW hasn't gotten your memo Aunty, because they are transferring even more hatchery fish to the select areas.

With careful thought and preparation (selection of hatchery release sites, etc) it is possible to craft fisheries that are successful in targeting prodimately hatchery fish in a specific location at a specific time. The Columbai River SAFE areas are an examples as well as the Tulalip bubble fishery in Puget Sound.

While such fisheries could be considered "selective fisheries" it is well to remember that in these cases it is the fishery itself and not the fishing method that is selective. In such fisheries virtually any method of fish capture can be used in the fishery and it would remain a "selective fisheries".

Tight lines
Curt

Agreed, it's the time and place that is selective, not the method of capture.
I'm not arguing that a better method of commercial harvest might be better, what I'm saying is relegating the gillnets to the SAFE areas while this method is found and perfected might be a better plan.
Status quo and business as usual for the commercials.

I see our interim Director as just another wheel that is turning to continue with the Status Quo. He whines about how the Tribes continue to favor lesser escapement.

IMHO the Tribal fishers would be right if only wild fish were to hit the gravel. This is far from reality given hatchery fish spawning without success in the wild.

Sg nailed it. Gill nets impact not just the target species. Similar size steelhead are encountered.

IMHO these are the larger wild fishes. The hens carry a chance to increase the spawner population due to the larger size, nourishment, of the offspring.

DFW gets all worked up over harvest. Sometime, they will see the error of thier ways.

Im starting to GET why Todd and some others are so tired of some of these issues.

Ickstream, you're late to the party. The final battle to eliminate gillnets and tangle nets has begun. You have been around long enough to see gillnet marks. Its time to pick a side.

Safe zones are not the answer.

For the record, my question had nothing to do with hatchery fish versus wild fish, although I realize that's the main issue in "selectivity."

I think my question about size selectivity has been answered (thanks Sg and others), but feel free to continue on about whatever else (thanks for the "advice" LB... I always forget to pick a side).

O. mykiss v H. sapiens

-IS

In apathy one condones the status quo through inaction.

IMHO gill nets represent the most harmful, least sustainable methods of commercial harvest. Much like the trawlers along our coast.

Life's what you make it.

Because that is the method that the law allows, the areas are set up and fully funded and operational. ODFW and WDFW have increased the number of smolt to these SAFE areas.
It satisfies the public right to the fish.
It would create an instant bridge to whatever harvest method that is developed in the future.
And last but far from least, it ends the status quo by eliminating the effects of gillnets in the mainstem.

The increase in the number of smolts has come from area's sportsmen fish and have been placed in the safe area's for the comercial fleet, so what part of this bill did you all pay? It will be interesting to see how this all works out. The biggest problem I have seen so far is that it has not got any nets off the mainstream. Lest i forget, The CCA and others are hard at work trying to change the laws regarding your gill nets. The dinasaurs have been gone a long time now..........Chuck G

So as long as it works in the CR then the rest of the salmon and steelhead, can go to hell.
If the fish are going to be designated for the commercial fisherman, he can get out of his boat and wander up to the hatchery. Whatever gets by us, he is welcome to have. Better yet, lets just let the public come by for their monthly quota of fish. That way we cut out the fisherman, processor and grocery store. The state can collect the cash on the spot. Five buck a pound ought to cover it.

Or it provides a instant end to the status quo mainstem gillnetting, creating a bridge so other methods of commercial harvest can be created.