Crustacean Station: HIA to Monitor Crab Stocks in Hoonah Harbor

Hoonah Indian Association (HIA) is starting a long-term crab population monitoring program in response to reported low Dungee harvests and the recent discovery of the highly-invasive European Green Crabs in Metlakatla, HIA has started using a new method of studying crab stocks in Hoonah Harbor. 

Dungeness crabs are facing a variety of environmental stressors–ocean acidification, warming temperatures and habitat loss—which can be made worse by overfishing and invasive species. Ocean acidification, caused by the ocean absorbing human-made carbon dioxide, raises the pH of the water and can damage crabs’ shells. A 2016 study by the National Oceanic and Atmospheric Administration found that the hair-like whiskers crabs use to sense their environments and navigate were being dissolved by the more acidic waters up and down the west coast. Without these whiskers, crabs will have a harder time avoiding predators and seeking out prey. A separate paper from 2017 found crabs may end up going hungry in the future, as environmental predictions for the year 2100 show clam and bivalve populations that form a large fraction of crabs diets declining with ocean acidification. If Dungeness follow the trend set by snow crabs, which saw absolute decimation in recent years (nearly 99% loss of female crabs over the past two years, driven by warming waters in the Bering Sea), then Dungees and the people who rely on them could be in deep trouble in coming years.

Example of a Dungeness megalopa. Dungeness pass through five stages of zoea and one as megalopae before settling to the bottom as juvenile crabs. After another two years on the bottom they reach reproductive age, and can live from 8 to 10 years if they successfully avoid crafty crab pots and hungry halibut. Photo courtesy of Shelly Trigg/NOAA.

Perhaps the most pressing threat to Dungees is the presence of the highly invasive European Green Crabs (EGCs) recently discovered in Metlakatla. Green crabs compete for the same food sources, eating up to 40 clams per day, and destroy eelgrass beds, which are critical nurseries for young Dungeness. While green crabs have yet to be detected in Hoonah, their progression up the west coast of the US and British Columbia seem to imply that their arrival in town is more a matter of when than if. For more information about EGCS and how HIA is going to be monitoring and developing a strategy to combat them, look here.

The newly deployed Crustacean Station in Hoonah Harbor. A five-gallon bucket houses the battery and provides flotation, while a light hangs down from the bucket into the trap body, which is constructed from a 5-gallon translucent water bottle and a collection of funnels. Feel free to check it out if you see it in the harbor, but please don’t move or remove it!

Despite the value, both economically and for subsistence use, of Dungeness crabs, there is no active stock monitoring by the State, and research on the problem hasn’t been conducted in Southeast since 2004. To fill in these gaps and allow for informed management of local resources, HIA has recently deployed the new Crustacean Station, a low-tech but hopefully high impact way of monitoring crab stocks in Hoonah Harbor. Crabs spent the first stage of their lives as free-floating larvae before settling to the bottom of the ocean, during which time they’re attracted to lights, just like moths. Researchers can exploit this behavior by using light traps, which use waterproof LED lights instead of a more traditional bait like herring to catch crabs. After floating in the harbor overnight, any the catch can be identified and enumerated, allowing us to understand the number and size of larval crab present, as well as keep an eye out for invasive species.

Larval crab recruitment rates at three different bays in the Swinomish Reservation in the summer of 2018. The project will allow for monitoring of how juvenile crab populations and development are changing as well as when the peak recruitment period occurs–warmer waters due to climate change may result in a shift of when the larvae are most abundant and how quickly they develop. Figure courtesy of the Swinomish Indian Tribal Community.

While our trap wasn’t constructed until the end of the larval recruitment period, results from the Swinomish Indian Tribal Community in Northern Washington imply that we have a lot of exciting things to look forward to next summer. With their network of traps, they could monitor how different species of crabs migrated around Puget Sound, and look at the general population size. At the peak of crabbing season, they caught over 180 larvae in a single hour! They also tracked the growth rate of the megalopae, measuring the width of each of the crabs they found each week to understand how quickly the crabs were developing throughout the summer. While their short baseline of data (they only started using light traps in 2018) means that they can’t yet draw conclusions about how their results are changing, given the way warmer waters tend to cause earlier development in other species, it’s safe to assume that they’ll see changes in those results in years to come.

Not only will the new trap allow for monitoring of Dungeness stocks and the effect invasive crabs might have on them, it will also be used to directly look for the early presence of European Green Crabs. EGC larvae have distinctive antennae that can be observed under a microscope to distinguish them from other types of crabs. While HIA is already planning on conducting targeted trapping and shore surveys to look for adult EGCs, finding their larvae could give us more time to plan a response to limit their spread and destruction.

An example of the by-catch from the light trap, with 2mm gridlines in the background. Many types of crustacean larvae exhibit phototaxis (attraction to light), so the trap can be used to search for invasive species (such as European Green Crabs) and for a more general understanding of the health and biodiversity of Hoonah’s waters.

We may not be the Ghostbusters, but this is a perfect example of how if you’re noticing environmental and subsistence issues, we want to be the ones you call. While the members of our team all enjoy getting out on the water and up in the woods, we only have so many eyes between us and really rely on community input to know what to focus on. If you have questions or concerns, give us a shout!

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