Lummi Nation samples zooplankton to improve crab management

Crab larvae
Crab Larvae K Neumeyer

The Lummi Nation is sampling crab larvae to improve harvest management and contribute to salmon marine survival research.

“Because of the reduction of other fisheries, crab is more important than ever for Lummi fishers or Lummi families depending on fishers for support,” said Evelyn Brown, Lummi fisheries analyst. “Without crab, the economic base from fishery income would take a sharp downward trend”

But crab management, as with other fished species, depends on good stock assessment and population information.

Crab Larvae Sampling
Crab Larvae Sampling

“Because of the critical nature of the crab resource, we need to have a better grasp on recruitment processes and what might have the biggest impact on future populations,” Brown said.

Some factors affecting recruitment – the process of a larva maturing to an adult crab – include unregulated, illegal or underestimated harvest, derelict gear, increased tanker traffic, increased pollution, climate change and invasive species.

“Most of these factors are interrelated,” Brown said. “For example, increased tanker or other large vessel traffic results in increased derelict gear due to entanglement or severing of pot lines. Increased vessel traffic and the human footprint result in increased pollution. Climate change could exaggerate effects of pollution and increase invasive species. Many of the factors directly or indirectly affect recruitment of larval crab.”

In response to the need for better crab recruitment information, Lummi Natural Resources staff built 15 light traps to collect crab larvae at sites in the tribe’s harvest area. A light inside the trap turns on overnight, luring zooplankton that are attracted to the brightness.

“A researcher in Oregon found a significant relationship between catches from light traps and the number of larvae that survive to reproductive age,” Brown said. “This year’s feasibility study was a huge success and we want to keep doing it. I think other entities will do the same and we plan to help other groups build traps and initiate larval crab monitoring”

Natural Resources technicians also sampled zooplankton, mostly crab larvae, in North Puget Sound by towing a bongo net at six marine sites and lowering a net vertically into a deepwater site.

One of the sampling sites is sponsored by the Salish Sea Marine Survival Project, managed by the nonprofit Long Live the Kings. The original goal was to better understand the relationship between juvenile salmon, especially chinook, and their plankton prey. Late-stage crab larvae are a mainstay for juvenile chinook, and in some areas may be critical to salmon growth and survival.

“The extended survey sites that are offshore from light trap sites will help determine how catches from the plankton tows might be related to catches in the light traps,” Brown said. “That way, we might infer trends from longer-term zooplankton sampling information.”

Data from all the monitoring sites will be shared with the Marine Survival Project.

“We want to continue to support collaborative efforts that help protect tribal rights and the environment they depend on, that engage many partners and citizens, and that do work that a single entity cannot on its own,” Brown said. “We are hoping the crab monitoring can become a collaborative effort, and look forward to developing partnerships.”