Offshore Juvenile Eulachon Growth and Abundance

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West coast Vancouver Island length frequencies by year, fishing ground and the Pacific Decadal Oscillation: Red = positive, Blue = negative (See latest PDO values).

eulachon length frequencies

Standard Length (mm)

Figure 1. Panels on the graph show eulachon length frequency samples collected at approximately the same date each year from four, offshore shrimp trawling grounds off the west coast of Vancouver Island from 1995 to 2015.

Typical bimodal distributions correspond predominantly to age 1+ (60-130 mm) and age 2+ (100-180 mm) juvenile eulachon and may also include some age 3+ (140-200 mm) and older fish shown on the right tail of the curves. In 2005, compensatory growth of age 2+'s is evident on each fishing ground during a low abundance, transitional year (negligible, age 1+ juveniles). Annual shifts in the modal lengths of age 1+ and age 2+ juvenile eulachon appear to correspond to changes in the Pacific Decadal Oscillation (PDO). Inter-annual growth of juvenile eulachon has increased incrementally during each 'cool phase' of the PDO and decreased incrementally during each 'warm phase' (phases are indicated by blue and red, vertical bars to the right of the graph). Part of these growth increments may also be indicative of year class strength (i.e. uncertain ages of the larger fish). Missing years (or panels) on the graphs indicate that eulachon L-F samples were not collected on some offshore grounds (e.g. the Pachena-grd in 1995 & 1997, Ucluelet-grd in 1995-1997, Tofino-grd in 2000-2001 and Nootka-grd in 1996 & 2001). Standard lengths (tip of snout to hypural plate) were measured to the nearest millimetre (mm) and are displayed on histograms with no pooling of length groups. Eulachon feed primarily on euphausiids and copepods. - B. McCarter


graph of WCVI juvenile eulachon abundance

Figure 2a. Eulachon biomass trends from 1995 to 2012 off the west coast of Vancouver Island as measured by annual, shrimp trawl surveys.   Data points are from BC Shrimp Survey Bulletins.

Eulachon abundance/availability indices were determined on four, offshore fishing grounds while conducting assessments for shrimp: Pachena and Ucluelet grounds (SA 21OFF+23OFF or SA 121+123), Tofino grounds (SA 124) and Nootka grounds (SA 125).

Eulachon catches 2004-2015

Figure 2b.  Eulachon catches during annual shrimp trawl surveys off the west coast of Vancouver Island (Maximum = 866 kg/tow). See also 1963-1999 mid-water trawl surveys.

 



Queen Charlotte Sound length frequencies by year, fishing ground and the Pacific Decadal Oscillation: Red = positive, Blue = negative (See latest PDO values).

eulachon length frequencies

Standard Length (mm)

Figure 3. Growth trends observed among eulachon samples collected in Queen Charlotte Sound from 1995 to 2013.   Modal lengths have shifted synchronously with those collected off the West Coast of Vancouver Island.

Juvenile eulachon inter-annual, size-at-age shifts are not as apparent in Queen Charlotte Sound (QCS) as those measured off the west coast of Vancouver Island. This could be a result of a slightly broader spatial and temporal pooling of L-F samples or perhaps, greater inter-annual, productivity modulation in Queen Charlotte Sound. Eulachon L-F time-series northward of these locations are incomplete but never-the-less, show striking similarities in growth patterns and trends (i.e. Chatham Sound, 1998-2004). Eulachon inter-annual growth patterns are more variable in southern offshore waters than in offshore feeding areas to the north where long-term population declines are not as apparent.

graph of QCS juvenile eulachon abundance

Figure 4a. Eulachon biomass trends from 1998 to 2012 in Queen Charlotte Sound as measured by annual, shrimp trawl surveys.   Data points are from BC Shrimp Survey Bulletins.

Eulachon abundance indices were determined on offshore fishing grounds while conducting assessments for shrimp on the Goose Island and Pearl Rocks fishing grounds in Queen Charlotte Sound. Eulachon relative abundance/availability indices and juvenile size-at-age variability appears to coincide with the Pacific Decadal Oscillation (see latest PDO values).

Eulachon catches 2004-2013

Figure 4b.  Eulachon catches during annual shrimp trawl surveys in Queen Charlotte Sound (Maximum = 785 kg/tow). See also 1963-1999 mid-water trawl surveys.

 

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