Turtle bycatch

When you’re standing knee-deep in a stream, branches growing together into a leafy green tunnel above your head, slippery cobbles under your feet, expecting to find a steelhead or two in the net you just jerked out of the water, it can be a little startling to see a five-inch crayfish staring back at you, waving its claws.

Sometimes at work, when I’m lucky, I get to step outside my office for a little while and help the graduate students in my lab as they collect samples and data in the field. The project I work on the most involves scooping up fish in hand-held nets, but occasionally we capture other things, too – organisms we weren’t targeting or trying to catch, like that five-inch crayfish. In the fisheries world, this accidental take is called bycatch. Usually when scientists and managers are studying or trying to regulate bycatch, they’re dealing with marine life, but it happens in freshwater fisheries, too – and not just with crayfish.

When I catch a crayfish in my net, I pull it out and set it back in the stream where it came from (carefully, to preserve my fingers), but that’s not always possible in other situations. Some fishing nets are set underwater, and left to soak and collect fish for several hours before the catch is retrieved; that can be a problem if air-breathing aquatic animals – like turtles – also get caught.

A team of Canadian scientists recently published a case-study of freshwater turtle bycatch in a small lake in the journal Aquatic Conservation: Marine and Freshwater Ecosystems. They estimated the effectiveness of two methods for reducing turtle bycatch in Lake Opinicon, in southeast Ontario, Canada, which supports a small commercial fishery: adding “exclusion devices” to fish net openings that would keep most turtles out but let fish in, and shortening the fishing season.

The researchers measured the shells of four species of female turtles, and found that the smaller exclusion device they evaluated (which had an opening about two inches wide) would keep most turtles out of the fishnets – between 92 and 100 percent of three turtle species in the lake had shells too large to fit through the device. For the fourth and smallest turtle species the scientists studied, however, the exclusion device was not as successful – only 27 percent of those turtles were bigger than the opening.

If managers close the fishery during the time when turtles are most active, that can reduce turtle bycatch; to evaluate the effect of closing the fishery a month earlier in the spring, the scientists measured how active the turtles were during May and June. Only one turtle species was most active right before the current closing date of June 20, but, as the authors note, “[w]hile seasonal activity rates vary among species, a shortened fishing season would still decrease the total number of turtles captured, provided that there is no compensatory increase in fishing effort.”

Based on demographic traits like the current number of turtles in the lake, how old female turtles are when they first reproduce, and the proportion of female turtles that reproduce each year, the researchers estimated how the population of each turtle species might increase or decrease over the next 500 years under different bycatch scenarios. They determined that for three of the turtle species, just one or two female turtle deaths due to bycatch each year could lead to a complete loss of the population from the lake within that timeframe.

When I catch a crayfish in my hand-held net I can let it go right away, but turtles caught in underwater fishnets don’t have that option. The unintended capture of turtles during fishing can have disastrous consequences – as the authors write, “it is imperative that appropriate bycatch mitigation measures . . . are put in place to ensure the long-term persistence of freshwater turtles.”

Researchers studied four turtle species in Lake Opinicon, in southeastern Ontario, Canada, including the painted turtle. 

(Image by Micheal Jewel via Flickr)

Beavers, planes and parachutes

In 1950, it cost Idaho’s Department of Fish and Game $30 to relocate four beavers via parachute. That included the cost of the boxes to hold the beavers, the parachutes, and flight time, according to a paper published that year in The Journal of Wildlife Management by Idaho Fish and Game Department employee Elmo Heter. The beavers were removed from habitats where they were causing trouble for humans – backing up ponds by building dams, and, in the process, damaging irrigation systems and orchards – and transplanted to places where they would “do much toward improving the habitats of game, fish, and waterfowl and perform important service in watershed conservation.”

Much of Idaho’s wilderness is inaccessible by road, necessitating long journeys on the backs of pack animals for relocated beavers before the plane-and-parachute method was developed. The new method was not only faster and easier for Fish and Game personnel (and, no doubt, the pack animals); it was also safer and less stressful for the beavers, which spent less time in transit and survived the subsequent relocations at a much higher rate.

Heter calls out one beaver in particular who made a direct contribution to the research. “Satisfactory experiments with dummy weights having been completed,” he writes, “one old male beaver, whom we fondly named ‘Geronimo,’ was dropped again and again on the flying field. Each time he scrambled out of the box, someone was on hand to pick him up. Poor fellow! He finally became resigned, and as soon as we approached him, would crawl back into his box ready to go aloft again.” In repayment for his services, Geronimo was released into the wilderness and reportedly established a successful beaver colony.

Beavers are still being transplanted today, and still for the same parallel reasons as in the past – to remove them from places where humans find them a nuisance, and to place them in areas where scientists and managers hope they can do some good.

New research published in the journal Aquatic Conservation: Marine and Freshwater Ecosystems by a team from the University of Helsinki in Finland suggests that beavers may indeed improve habitat for other animals. The scientists studied a series of 28 ponds, half of which were naturally colonized by beavers, and found that beaver activity – primarily flooding due to dam building – resulted in more waterbirds overall, as well as a more diverse waterbird population. The flooded ponds had about seven times as many insects – a prime food source for waterbirds – and were also shallower than the beaver-less ponds, both of which, the authors suspect, made the beaver ponds a more desirable habitat for waterbirds.

Where beavers move in, waterbirds tend to follow – and sometimes the beavers don't need a plane ride and a parachute to get there. 

Beavers fell trees, sometimes of considerable size, and combine them with mud and branches to build their dams.

(Image by D. Gordon E. Robertson via Wikimedia Commons)