Comparing Stock Assessment Methods for Pacific Herring
University of Toronto researchers are reviewing stock assessment methods for Pacific herring. Stocks of Pacific herring are in decline in three of their five major regions of distribution in BC despite fishery closures during years of low abundance. This project seeks to understand the causes of these declines by quantifying support for various alternative hypotheses; for example, whether declines are driven by competition, disease, climate, and/or fishing. By reviewing stock assessments across different regions, researchers aim to determine whether the selected methodologies produce stock estimates directly comparable in analyses of herring population dynamics.
Bioeconomic Dynamics of Fisheries and Aquaculture
Melissa Orobko recently completed her Master of Science degree at the University of Toronto investigating the relationship between wild fisheries and aquaculture. A shortfall in wild seafood supply to meet growing demand has led to the rapid growth of farmed fish populations. Wild fisheries and aquaculture can interact ecologically (e.g. through sharing of diseases) as well as economically by supplying similar products to markets. Melissa’s research involved developing and analysing mathematical bioeconomic models of fisheries and aquaculture, and showed that alternate stable states of either aquaculture or fishery dominance are likely to exist, and transitions between the states can be abrupt and difficult to reverse. Coexistence of fisheries and aquaculture is therefore either unstable or requires ecological feedbacks be kept below a threshold. Empirical records of salmonid production are in qualitative agreement with model outputs, implying that careful management is required to sustain wild fisheries into the future.
Modelling Spread of Sea Lice between Salmon Farms
MSc candidate Peter Harrington of the University of Alberta is investigating the spread of sea lice between salmon farms. In the Broughton Archipelago, sea lice can spread between salmon farms either by hitching a ride on migrating wild salmon or simply by floating through the ocean as nauplii. Therefore, if a single farm experiences an outbreak of lice and subsequently treats the farm to remove the infestation, some lice will have already reached other farms before the treatment has taken effect. This project uses mathematical models to examine how times for first passage of sea lice past farms are influenced by different environmental factors, such as extent of mixing in the ocean due to tides or size of salmon farm. The goal is to see how quickly lice from an outbreak will spread to other farms, with a view to adjusting treatment protocols to minimize subsequent outbreaks and dispersal. Because many salmon farms in Broughton Archipelago are owned and operated by a single company, this research has significant potential to inform local management practices.
Links between Juvenile Salmon Leaping Behaviour and Presence of Sea Lice?
Undergraduate student Emma Atkinson from Simon Fraser University in Vancouver sought to investigate questions surrounding the leaping behaviour of juvenile salmon. Juvenile salmon leap frequently, but no one knows why. One key hypothesis is that they may leap to dislodge ectoparasites such as sea lice, which is likely to be energetically costly for the salmon and potentially compromise their health and survival. Building on a study published in 2007 where juvenile salmon infected with sea lice exhibited a 14-fold increase in leaping behaviour compared to uninfected fish in a laboratory setting (Webster et al. 2007), this ongoing project is examining under natural conditions whether leaping behaviour is effective at dislodging sea lice. Six multi-day trials were conducted and post-trial louse loads were measured and compared on fish free to jump versus fish prevented from jumping. Data are currently being analysed to increase understanding about this aspect of juvenile salmon behaviour.
SLICE: Policy & Regulation
Undergraduate student Griffin Kelly from the University of Toronto examined use and regulation of SLICE, an insecticide used by operators of salmon farms to manage sea lice populations on their farms. A main area of interest was the impact of SLICE use on natural resources and environment legislation. The researched assessed non-chemical alternatives to SLICE, such as incorporating cleaner fish and filter feeders into farms to reduce lice levels, as well as the importance of collaborative monitoring practices and the need for coordinated regional policies for lice management. In addition to policy research, a series of SLICE efficacy bioassays were conducted on sea lice collected from wild juvenile salmon. These data will be compared to results for previous and future bioassays by Salmon Coast Field Station researchers in order to monitor potential resistance to SLICE.
Species-specific Leaping Behaviour by Salmon
Many observers of adult Pacific salmon are convinced each species exhibits unique leaping behaviour. However, it is not known whether juvenile salmon also exhibit unique leaping behaviours. Undergraduate student Jack Goldman from the University of Toronto used slow-motion video imagery to record and classify leaping by sockeye, pink, and chum salmon smolts, and determine whether species of juvenile salmon can be identified by unique leaping behaviour or characteristics. Initial data indicated many similarities between species for metrics such as roll and sideways rotation, wag, leap height, and body orientation at water exit and re-entry. Further analysis of other leap characteristics will aim to identify distinguishable leaping behaviour between species.
Sea Louse Host Selection
From years of field observations Salmon Coast researchers have noted that compared to pink salmon and chum salmon sampled in the Broughton Archipelago, sockeye salmon migrating through Johnstone Straight have relatively high numbers of Caligus clemensi sea lice. Caligus spp sea lice are marine ectoparasites occurring naturally on many species of wild fish. This preliminary research, conducted by undergraduate student Yijun (Lily) Xiong of the University of Toronto, explored whether Caligus are likely to be more abundant in the southern waters sockeye migrate from, and/or whether these lice prefer sockeye salmon to pink or chum. A small-scale pilot study of host selection by C. clemensi found that lice attached faster and in higher numbers to sockeye salmon than to pink salmon, suggesting possible preference and the value of further investigation.