Big Indiana Bass

This post is a great example of why I love the Internet. It starts out with an observation I've made several times over the past 10 years or so while bass fishing, that being the prevalence in some waters for bass to have very small leeches attached inside their mouths. Cool thing I noticed, but never thought much more about it. Then recently I stumble upon this piece of research and the lightbulb goes off - this is what I've been seeing.

High prevalence of buccal ulcerations in largemouth bass, Micropterus salmoides (Centrarchidae) from Michigan inland lakes associated with Myzobdella lugubris Leidy 1851 (Annelida: Hirudinea).

Faisal M, Schulz C, Eissa A, Whelan G.

Widespread mouth ulcerations were observed in largemouth bass collected from eight inland lakes in the Lower Peninsula of Michigan during the summer months of 2002 and 2003. These ulcerations were associated with, and most likely caused by, leech parasitism. Through the use of morphological dichotomous keys, it was determined that all leeches collected are of one species: Myzobdella lugubris. Among the eight lakes examined, Lake Orion and Devils Lake had the highest prevalence of leech parasitism (34% and 29%, respectively) and mouth ulcerations (53% and 68%, respectively). Statistical analyses demonstrated that leech and ulcer prevalence varied significantly from one lake to the other. Additionally, it was determined that the relationship between the prevalence of ulcers and the prevalence of leech attachment is significant, indicating that leech parasitism is most likely the cause of ulceration. The ulcers exhibited deep hemorrhagic centers and raised irregular edges. Affected areas lost their epithelial lining and submucosa, with masses of bacteria colonizing the damaged tissues. Since largemouth bass is a popular global sportfish and critical to the food web of inland lakes, there are concerns that the presence of leeches, damaged buccal mucosa, and general unsightliness may negatively affect this important sportfishery.

Then, of course, finding one study leads to a list of references and more searching, and I find another paper;

• Epidemic oral ulceration in largemouth bass (Micropterus salmoides) associated with the leech Myzobdella lugubris

which backs the first one nicely, actually coming out much earlier and from the east coast, and assures me this is what I've been noticing. The cycle continues as I now learn that this particular leech is highly present in the freshwater fishes of Lake St. Clair;

• Leeches (Annelida: Hirudinida) Parasitizing Fish of Lake St. Clair, Michigan, U.S.A.

and most recently, this leech was found to be able to harbor the disease Viral Hemorrhagic Septicemia virus (VHSV) and is highly likely the/a vector for the transmission of this fish killer;

• Detection of Viral Hemorrhagic Septicemia virus (VHSV) from the leech Myzobdella lugubris Leidy, 1851

which brings this story full circle for me, as this disease and the subsequent federal ban on transportation of game fish from and between Great Lakes states several years back was the reason we didn't get our local lake stocked that year with fish from a hatchery in Wisconsin that I had ordered. It really is a small world after all...

Long-Term Changes in Recreational Catch Inequality in a Trout Stream

David A. Seekella, Chase J. Brosseaub, Timothy J. Clinec, Raymond J. Winchcombed & Lee J. Zinnce

We've covered the topic of catch inequality before, the theory or statement you hear all the time about 10% of the anglers catching 90% of the fish. You can find that original piece in our articles section with the title, MythBusting: 10% of Anglers Catch 90% of Fish. It talks about Gini coefficients, Lorenz curves, and other fancy terms researchers use to describe and model this axiom. This new paper looks at catches from a single body of water over 20 years during a significant period of decline in catch per unit effort (CPUE). In other words, the fishery kept getting tougher as less fish were caught in any given year for the same or increased amount of fishing effort. The hypothesis on the table was whether between-angler inequality increases as catch per unit effort declines. That is, do we see an even bigger differences between catches of very skilled anglers and less skilled anglers as a fishery gets worse.

Without getting into too much scientific gore, researchers found that "catch per unit effort still plays a critical role in determining the magnitude of catch inequality."  That is, on lakes where the average number of fish caught by an anglers per hour of effort is high, catch inequality is low. On the other hand, when fish captured are few and far between, greater inequality exists among anglers, or a small percentage accounts for a majority of the fish caught.

The new and interesting result coming out of this study was that trip-to-trip inequality increases with declining catch per unit effort, but between-angler inequality changes very little. Between angler inequality does go up, but not significantly. It's trip-to-trip inequality that accounts for the significant difference. I'll try and put that into simpler terms.

In any given year on a body of water, you have a range of anglers representing all levels of skill and ability; some really good, some not so good. From year to year, individual anglers fishing a body of water may change, but overall you pretty much keep that same general percentage level of both skilled and unskilled anglers in the pool. There's always some good anglers and there's always some not so good, 5 years, 10 years, even 20 years later. As such, inequality between anglers when assessed over the entire angling population over time remains a relative constant. It would be similar to saying that if you looked at the average age of anglers 5 years ago, versus say 5 years from now, it probabaly wouldn't be a whole lot different. There will always be a mix of both young and old anglers, and that age difference between them doesn't change much over the course of time.

What did change significantly though was trip-to-trip variability. So as the fishery went downhill, catching that fishery on a "good day" became much more important than the relative skill level of anglers on that body of water. Catching it on a "good day" equated to environmental randomness. As the researchers stated, this "explains why, on any given trip, a weak angler can be more successful than a skilled angler." It's the 'sucker shot'  played out. Example: you may be an above average fisherman, but the last time you hit "the dead sea", you had blue sky cold front conditions and a 15 mph north wind - you caught some fish, but overall fishing sucked. Your buddy, who isn't near the fisherman you are, hit "the dead sea" on a good cloudy, drizzly day with light winds as a slow moving front was approaching - he wacked them. It really had little to do with his ability, but rather more to do with his timing.

And so this was the end result of this particular piece of research. As a fishery gets tougher and tougher over the years (CPUE declines), catching that body of water "on a good day" becomes the more significant reason for angler inequality among catches. The trick then lies in getting very good at predicting when the "good days" will be (the 'sucker shot'), or simply going every chance you get so when the good days occur, you'll already be there.

**David A. Seekell, Chase J. Brosseau, Timothy J. Cline, Raymond J. Winchcombe & Lee J. Zinn (2011): Long-Term Changes in Recreational Catch Inequality in a Trout Stream, North American Journal of Fisheries Management, 31:6, 1100-1105