Ben,
Is there any information about the correlation of age/fertility in perch? It's common for people to preach - throw back the big spawners but I have often wondered if that's correct. I was shocked to hear at a walleye's for tomorrow meeting that the biggest female walleyes (25"+) are the least productive spawners.
In general, two things are true: larger and older females have more eggs (and/or produce larger sized eggs) than smaller/younger females. And also after a certain point in the lifetime of an individual fish, the viability of said eggs begins to drop off as the fish ages. But the age or length at which that happens may vary from population to population and likely even from fish to fish.
The limited studies that have been done on perch in Lake Michigan show that larger females produce both more eggs, and larger eggs than smaller perch. Larger egg size has been linked to better survival to larval stage in some cases. But in other cases, older/larger females actually had lower survival of their larvae. Fish aging (senescence) and maternal effects are complicated subjects and understanding the nuances in each population is tough.
You also have to be careful interpreting what people say regarding reproductive capacity (fecundity), because there is individual fecundity, and then population fecundity. Imagine a bell shaped curve, where for the sake of this conversation, adult walleye numbers peak in the low-to-mid 20 inch range, and dwindle quickly as length increases over 25 inches. In this hypothetical situation, there's nearly 10x the number of walleye in the 20-25 inch length range as there are in the 26-31 inch range. Which makes sense - usually longer walleyes are older, and there are fewer of them that live to old age than middle age.
As a group, 20-25 inch walleyes probably contribute more to spawning than does a 26+ inch walleye, through sheer numbers advantage - a 26-31 inch walleye would have to have 10x the individual success rate of its eggs compared to a 20-25 inch fish, just given the sheer number difference in population between those to groups. But as an individual, it may be that a 26+ inch fish has more eggs that make it to the fry stage. All that to say, it could be very correct to say that large walleyes are the best spawners, but also the least productive in contributing as a whole to a given cohort of walleye, just because there are way fewer large walleyes compared to medium size walleye
BNature post=41926 userid=717
In a lake the size of Lake Michigan, it's doubtful that regulated sport angling would negatively affect the perch population. A relatively few spawners surviving the perch-jerkers can produce an abundant amount of perch fry to repopulate the lake. The rub is the conditions the newly hatched perch have to endure to grow into keeper sized and eventually jumbo sized. If the number of jumbos drops off it's for two reasons. 1) Someone caught them. 2) They died from old age. By far, the second reason is the most common.
Actually, fisheries managers would prefer the jumbos get caught by recreational anglers. By the time they've reached 13 to 15 inches, they've probably spawned three or four times which (in ideal conditions) should result in a stable or even expanding population.
The biggest thing is recruitment. If we have consistent spawning success, lots of angler harvest is not a big deal, because there's constant replenishment of perch via spawning. However, the danger zone is if there's lots of angler harvest (particularly of larger females) followed by several years of poor spawning success, so there aren't younger generations growing up behind those large females. And the story in Lake Michigan, post-mussel invasion, is that recruitment is very hit-or-miss. We'll have a few years of bust spawns, followed by a really good one, and then another couple of bad ones.
Since perch lay lots of eggs, and the spawning success seems to be driven much more by environmental conditions post-spawn than it does by the number of spawning perch, it is unlikely that perch spawning success is altered much by angler harvest. In fact, 2015 was the biggest spawning year in history, even back to the 1970s and 80s - and there are way fewer adult perch in 2015 compared to back then.
That said, uncertainty is always the biggest factor in fisheries management. We don't know the true perch population size. We don't know future spawning success. We don't know the current angling mortality rate. We have to make reasonable assumptions based on the best available data.... and right now we're still seeing some decent spawning success despite the last few years of heavy winter perch harvest. I think it is likely that whatever conditions have led to fast growth and larger perch have also allowed for reasonable spawning success
