The image below is a screen cap of the cover page of what is probably my favorite surfperch paper. I’ve learned a ton about surfperch natural history from the material Darrell Pruden put together for this report. Darrell’s retired now and I hope he knows how important this work is to all of us surfperch junkies.
Pruden examined scads of surfperch carcasses that he obtained from friendly sport fishers. He was able to record life history information about the recreationally significant members of the surfperch family, Embiotocidae, that live in northern California and all the way north to Vancouver Island, BC and beyond. Below, I show two figures that summarize some things Pruden learned about redtail surfperch, Amphistichus rhodoterus, in southern Oregon.
By examining otoliths, Pruden found that redtails live to 13 years and beyond, I didn’t expect that. The average size 1-year-old in his sample is about 165 mm (fork length); that’s about 6.5 inches. And, at pretty much all ages, females are larger than males.
Pruden also found that most of the fish anglers take are 3 to 5 years old and females make up the biggest proportion of the catch in all age classes. If this has got you fired up, check out the rest of Pruden’s report.
Pruden’s life history information is great background for the remainder of this post, which is more or less about 1-year-old and younger redtails.
About three weeks ago, in Finding Fish: Do Tides Matter, I wrote about tides and redtail surfperch abundance in the surf zone. I showed there wasn’t a strong signal linking tidal attributes like height of high and low tide, and swing to redtail abundance in the surf. There are plenty of other environmental factors that might help explain redtail abundance; things like surf conditions and phase of the moon, for example, but I haven’t evaluated these. For now, the best predictor of redtail abundance I’ve examined is month of the year.
I showed evidence from my previous sampling, including the results summarized in the chart above, suggesting high surf zone abundance of redtails in September and low redtail abundance in the spring, especially April and May. Because I kept track of sexes and age classes of all fish in the sample, it is possible to take a detailed look at abundance, and maybe get some new insights about the life history of redtail surfperch.
I classified each individual into one of the following categories: male, female, subadult, juvenile, or unclassified. Males and females are adult fish. I described how to tell adult males from from adult females in Boy Meets Girl. We still don’t know how old redtails are when they mate for the first time but Pruden showed that redtails can live a long time, so this group includes fish from several year-classes. Subadults are nearly-adult fish that are sexable by external characteristics but I lump males and females together here; these are most likely the 1-year-olds in Pruden’s sample. Juveniles are young fish, smaller than Pruden’s 1-year-olds. They are too small to be retained by anglers. These young fish are impossible to sex in the field and release safely. Thus, the sexes are lumped in this category. I discuss the fine points of identifying juvenile and subadult redtails in Boy Meets Girl Revisited. My Unclassified category is not a life stage or sex but a thinly populated category of fish that escaped before I was able to determine the sex or life stage. The composition of the catch is shown in the chart below.
Before I discuss these results, there are two pieces of background information worth mentioning. First, females give birth, in the surf, to live young between mid-August and mid-September. Second, my sample sizes are kind of small so I don’t want to make too much out of it. The chart above summarizes my observations of 185 redtails; a small sample, but until somebody comes up with a better characterization, it’s what we’ve got.
My first observation about the composition of the catch is the high frequency of adult fish in the August and September catch. To a fisherperson this means a higher proportion of bigger fish. That’s what fishers want, right? If you hang out on the beach much you know that August and September is prime-time for redtail angling. This is the period when you can expect more bigger fish in the surf, so it makes sense to see more angler effort in August and September. There is one interesting difference between Pruden’s results and mine. If I’m reading it right, Pruden’s Figure 10 (above) shows that females are more prevalent in the catch whereas my catch is generally dominated by males. Maybe I can explain the female-bias in Pruden’s sample. Pruden’s Table 3 (above) reveals that females are bigger than males at all ages. Recall that Pruden got his sample from anglers. Is it possible anglers high-grade the catch, releasing smaller fish which tend to be males? It’s a possibility, but the male-bias in my sample begs a different explanation.
All of this raises a bunch of questions, like why no juveniles and so few subadults in August and September? Subadults dominate my catch in December and January, and are pretty well represented from October through April. This makes their absence from the May – August samples intriguing. Finally, I want to understand the high proportion of Juveniles in the November catch. Are those the rapidly growing babies born in August and September? They would be, at most, about 4 months old. I don’t know why juveniles periodically drop out of the sample, and I would love to know the age of the fish that transition from juveniles to subadults and from subadults to adults.
The Oregon Department of Fish and Wildlife continued to collect surfperch carcasses from willing anglers after Pruden’s 2000 report was published. I even donated a few to the cause and was rewarded with this nifty full-on grandpa-style corduroy trucker hat. In fact, I have a couple and I’m proud of them. Anyone out there want to venture a guess about the identity of the surfperch featured on my hat?