Survey and Experiment Design
Thalassia has planned and implemented experimental designs for a variety of marine ecology projects, including the research of Pacific herring spawning behaviour, lingcod habitat restoration, eelgrass transplant methodologies, and habitat impacts caused by marine structures. Our research experience includes projects throughout coastal British Columbia, from remote locations on the Central Coast to industrialized harbours in the Port of Vancouver.
Thalassia is working with coastal First Nations throughout BC to monitor ecosystem indicators, including canopy kelps, seagrass, Pacific salmon, and oceanographic parameters. Monitoring these indicators can simplify the evaluation of complex and dynamic marine ecosystems, providing an adaptive approach to managing human activities that seeks to ensure the coexistence of healthy, fully functioning ecosystems and human communities.
Recent Research: Causes and Consequences of Pacific Herring Deep Spawning Behaviour
Master's project completed with the Coastal Marine Ecology and Conservation lab at Simon Fraser University:
Thompson, M.D., Okamoto, D.K., Frid, A., Salomon, A.K.
Pacific herring are spawning on bedrock walls to depths exceeding 40 meters.
Deep spawn was found in areas with low boat traffic and low predator abundance.
Deep spawn egg survival was very low; most of these eggs were unfertilized.
Experimental evidence shows that the survival of fertilized eggs declines by 20% at 30m when compared with eggs at 3m.
What is deep spawn and why are we interested?
Since 2013 Heiltsuk fishermen and DFO survey divers have been finding unusually deep herring spawn on the central coast, often exceeding 30 or more metres in depth. These deep spawning events raised concerns that herring may be shifting their behaviour in response to fishing pressure and vessel activity, rising sea surface temperatures, or recent increases in predator abundance. Moreover, if the survival of herring eggs declines with depth, these changes in spawning behaviour could affect the health of herring populations.
What is causing deep spawn?
Local ecological knowledge from fishermen in Bella Bella provided several potential explanations for increases in spawn depth:
herring may be spawning deeper to avoid high numbers of predators (sea lions and whales),
increasing noise from boats and fishing activity may be scaring herring into deeper water, and
increasing ocean surface temperatures on the central coast may be causing herring to move deeper to spawn in cooler water.
To test these ideas we surveyed spawn conditions, including water temperature, boat traffic, and predator abundance in Spiller Channel, Higgins Pass, and Kitasu Bay during the 2016 herring spawn.
Our survey found that spawn depths increased when herring spawned in large numbers (millions of fish) in locations with deep bedrock habitat. We found support for these observations using historical DFO spawn data, showing that herring tend to spawn deeper in Spiller Channel during years when fish abundance is high. On our survey, deep herring spawn (exceeding 30 m) was found covering rock walls along 2.5 km of shoreline in north Spiller (see map below). We only found this deep spawn in areas with low vessel traffic and low predator abundance. No evidence was found for deep spawn caused by differences in sea surface temperature.
What are the consequences of deep spawn?
Deep spawn egg survival in Spiller Channel was very low (< 10 %), and we suspect that most of these eggs were unfertilized. In addition to these experiment observations, we conducted a depth experiment to test for differences in egg survival with increasing depth. Kelp blades covered in herring eggs were transplanted to three different depths (3, 15, and 30 m) and collected for analysis after 9 and 15 days (just before they hatched). The survival of herring eggs declined by 20% at 30m, in comparison to eggs at 3m. The reason for this decline in survival remains unknown, but may be related to reduced water flow in deeper water. In combination, we can infer from the survey and the experiment that eggs deposited at deep depths during a herring spawn have a severely reduced chance of survival.
Why is this important?
Our findings, when considered in context with work completed by Anna Gerrard in 2014 suggest that these deep spawning events may continue, and possibly increase in occurrence. Through interviews with Heiltsuk knowledge holders Anna found that herring spawning areas have both declined in number and moved away from the outer coast. If these trends continue, herring spawn may become more concentrated into deep fjords like north Spiller, where spawning events have been observed occurring on deep bedrock walls. This threat can be managed with risk-based fisheries strategies that account for distinct herring populations throughout the central coast, preventing over-harvest and allowing for recovery when population numbers are low.