April 5, 2010

Bassmasters Rejoice: Higher Temperatures Mean Bigger Fish

Here is the question of the day – who is Kevin VanDam (KVD)? Have a look at the picture below and now think about the question. Come on … admit it to the world – you have watched bass fishing on ESPN stations and you know that KVD is one of the world’s best bass fishermen. KVD has won the Bassmaster Classic three times (2001, 2005, and 2010) and many would argue KVD is simply the greatest bass fishermen who has ever lived. Leading pro bass fishermen are well paid (KVD won $500,000 for the 2010 Bassmaster Classic alone), they are well-sponsored, they have their own TV shows, iPhone apps, and video games, and they endorse countless products in the bassmaster line. Top anglers are superstars in their sport, and if you haven’t heard, pro bass fishing will be the next NASCAR (time will tell). The stuff is on TV all the time, and if you want to see KVD in action (and 1,000s show up for the pro events), there are events all over the USA – get into the sport and follow the women’s tour and junior’s tour as well! If KVD can win millions, why can’t you?

World Champion Kevin VanDam and a couple of live, freshly-caught largemouth bass
(Micropterus salmoides)

The problem is simple – bass fishing is apparently a lot harder than it looks, and your chances of beating professional fishermen at their sport are about the same as you beating Tiger Woods in golf, Pete Weber in bowling, or Garry Kasparov in chess (you don’t have a chance). Largemouth bass have acute senses of hearing, sight, vibration, and smell to attack and seize their prey, and if the prey happens to be your lure, get ready for a great fight. The fish often become airborne in an attempt to release the hook, and they definitely put on a great show for ESPN audiences during the fishing tournaments. Furthermore, they are remarkably hardy and if handled with reasonable care, they respond well to the “catch and release” rules of the pro fishing circuit; many studies have shown specimens which have survived being hooked and released multiple times. The two fish in the picture above will live to fight another day!

OK – you must be wondering what this fish story has to do with climate change, global warming, greenhouse gases, cap and trade, or some other topic of interest to us at World Climate Report. We are guessing you do not read Ecology of Freshwater Fish all that regularly, but if you did, you would have seen an article with the intriguing title “Climate–growth relationships for largemouth bass (Micropterus salmoides) across three southeastern USA states”. The article is by a biologist at the University of Mississippi and the work was funded by the USDA Forest Service, the Georgia Department of Natural Resources, an Alabama Academy of Science grant, and the University of Alabama, Department of Biological Sciences, and the University of Mississippi, Biology Department. Bass in the South is big business!

The research was conducted by Andrew Rypel who was basically interested in how climate variability and climate change might impact the ecology of freshwater fishes, and in his case, largemouth bass. Rypel states that “Adult largemouth bass populations were sampled from six rivers and seven reservoirs throughout southeastern USA during the summer and autumn of 2005–2008.” Unlike the fish caught in the Bassmaster Classic, we learn that “Each fish was measured, weighed and stored on ice for transport back to a laboratory. In the laboratory, otolith sagittae were extracted, sterilised in isopropyl alcohol, and stored in coin envelopes prior to incremental growth analysis.” The sagittae is one of three pairs of otolith that grow just behind the eyes; like tree rings, fish add annual growth increments that can be preserved over the lifetime of the fish. Given a lifespan of up to 20 years, the fish preserve a pattern that is related to their growth rate on an annual basis. Presto! Just like magic, the fish can tell us about good and bad growth years in the past.

Rypel reports “A total of 397 largemouth bass were collected and analysed from six rivers and seven reservoirs for interannual growth. Following detrending, synchronous annual growth patterns were revealed for largemouth bass within and among study systems.” The correlation coefficient between the different growth series averaged +0.62 “thus growth chronologies of individuals correlated well with growth chronologies of other individuals from the same populations.”

Now for the climate link. The author states “For each site, historical climate data were obtained from the closest available weather station from the Southeast Regional Climate Center. Data collected included mean annual and growing season values for air temperature, maximum air temperature, minimum air temperature, and precipitation total. For riverine sites, climate data were supplemented with mean annual and growing season discharge data from each river from the U.S. Geological Survey. For each river, the closest available streamflow gage to the collection site was used.”

Rypel used statistical methods common with the tree-ring crowd to link climate variations with growth of the largemouth bass. He found “Among six rivers and seven reservoirs in Georgia, Alabama, and Mississippi, strong correlations between annual bass growth indices and climate were detected. All but two ecosystems exhibited the following pattern: annual bass growth was significantly negatively correlated with annual precipitation metrics, and significantly positively correlated with annual temperature metrics. That’s right, the higher the temperature, the faster the bass grow. Based on multiple regressions, climate, on average, accounted for ~50% of variability in bass growth, although these values ranged from 28% to 65% depending on the ecosystem.”

Putting his work into context, Rypel states “Climate–growth relationships for largemouth bass in the southeast have practical implications for fisheries management. Achieving fisheries management goals (e.g., trophy fish production, high relative conditions, time-to-maturity) is highly desirable and can result in large community revenues.” He notes that “a single trophy largemouth bass fishery in Texas generated ~27.5 million US dollars annually and created 163 new jobs.”

The bass are telling us loudly and clearly – warmer is better for bigger fish! And from our perspective and certainly the perspective of Kevin VanDam, bigger is definitely better!


Rypel, A.L. 2009. Climate–growth relationships for largemouth bass (Micropterus salmoides) across three southeastern USA states. Ecology of Freshwater Fish, 18, 620–628.

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