Offshore Juvenile Eulachon - West Coast Vancouver Island

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eulachon length frequencies

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Graphs

Graphs

Graphs

Graphs

Figure 1. Length frequency (L-F) histograms of juvenile eulachon measured off the west coast of Vancouver Island during late April and early May from 1995 to 2016.

The surveyed areas where L-F samples were collected comprise the summer feeding grounds of eulachon as well as many other pelagic and bottom fishes concentrated on the productive banks, offshore of Barkley and Clayoquot Sounds. Typical bimodal distributions correspond predominantly to age 1+ (60-130 mm) and age 2+ (100-180 mm) juvenile eulachon and also may include some age 3+ (140-200 mm) and older fish shown on the right tail of the curves. Age 0+ fish are under-represented in these samples because young-of-the-year (YOY) are either, not yet present on the offshore grounds or they are too small and fragile to be captured intact in a shrimp trawl net. Eulachon in the Columbia River, spawn primarily in February while Fraser River eulachon, spawn primarily in April with immediate out-migration of 5-6 mm larvae into the lower Strait of Georgia occurring from late April to early June. Eulachon stock delineations have been investigated using life history, meristic, chemical and genetic traits. Various degrees of geographical separation and isolation are evident as populations appear to be adapted to each river-marine estuarine complex (clusters of adjacent, glacier-fed rivers and/or tributaries). It is also important to realize that first year seasonal growth of Fraser River eulachon is generally, 1-2 months behind that of other, more numerous, spring spawning pelagic/forage fish species such as Pacific herring which hatch (in the south) earlier and closer to extensive, inshore feeding areas (i.e. herring larvae occupy the entire perimeter regions of the Strait of Georgia as oppose to larval eulachon confinement to the southern strait and Gulf Island areas near the Fraser River plume). Relatively rapid advection of eulachon larvae and post-larvae southward and seaward towards Juan de Fuca Strait is highly probable and is supported by incidental plankton net catches of larger (25-30 mm) larvae in the strait by previous researchers.

Small-mesh, shrimp trawl nets and consistent fishing protocols were employed for each of these annual, offshore shrimp surveys where juvenile eulachon L-F samples were collected. Notice the very poor, seasonal growth indicated by the position of the year-class modes (or peaks) along the x-axis during the years, 2003 to 2005 (red vertical lines - positive PDO) and subsequent signs of improvement in growth shown from 2006 to 2009 (blue vertical lines - negative PDO). Some eulachon > 170 mm that were captured in 2003 and 2008 are likely age 3 and older individuals. Also note the very low proportion of age 1+ juveniles in May of 2005 and 2010 (unimodal distribution of small, age 2+'s) and high proportions of age 0+'s measured inshore, in Barkley Sound in 1998. Standard lengths (tip of snout to hypural plate) were measured to the nearest millimetre (mm) and pooled by 2 mm groupings on the histograms. Compare the length frequencies of Fraser River spawners (2001 to 2004) with offshore WCVI-rearing, juveniles (1995 to 2014) and investigate possible relationships with ocean conditions.

graph of eulachon length frequencies


Figure 2. Length frequency histogram and estimated ages of all eulachon measured off the west coast of Vancouver Island from 1995 to 2015 in early May.

Most eulachon were captured during late April to mid-May. Eulachon ages have neither been validated (i.e. a physical tag inserted in conjunction with an injected chemical growth marker deposited in an age structure or otolith) nor intensively researched and only a few hundred of the measured juveniles shown in the graph above, have been aged. Preliminary ages, often do not match consistently with statistically expected size. Aging errors are likely attributable to the counting of false annuli. As most eulachon are believed to be relatively short-lived, length-based methods may be more appropriate and practical. See recent eulachon age-at-maturity and stock identification research.

map of eulachon distribution off SW Vancouver Island

Figure 3. The distributions of eulachon captured off the coast of Vancouver Island as depicted by a series of 30-minute, research mid-water trawls (primarily from F.H.C. Taylor et al. G.B. Reed 1963-1985 cruises, A.P. Knight 1971 cruises, supporting chartered, commercial vessels and W.E. Ricker 1986-1999 cruises).

These pelagic trawl tows are a completely different series and method of trawling than those of the 1973 to 2014, shrimp trawl research surveys where eulachon L-F samples have been collected in more recent times (Figures 1 & 2). Blue circles are proportional to eulachon catches (kg). Red crosses indicate trawl tows where no eulachon were captured. Numerous exploratory trawl tows from other research cruises where no (or negligible) eulachon were captured are not plotted on the map. Eulachon catches (most < 850 kg) were recorded along the edges of offshore banks (80-180 m depth) and in the basins and canyons between offshore banks from March to October. Juvenile eulachon were also captured in shallower, inshore areas (e.g. Barkley Sound). Most eulachon were captured when mid-water trawl nets (e.g. Engel & Diamond #5, #7 & #8's) were fishing close to the sea floor and targeting on Pacific herring (one inch, mesh liners were installed in the cod-ends). Eulachon that are shown in Juan de Fuca Strait were trawled during fall and winter, herring hydro-acoustic surveys in the 1970's when large schools of mid-water fish (e.g. herring, dogfish, hake and eulachon) were highly mobile and migrating along the strait. Each fishing location (center of circle) was plotted using SYSTAT software where the areas of circles were set proportional to catches (kg).

map of BC eulachon distribution

Figure 4. The distributions of eulachon captured off the coast of British Columbia as depicted by a series of 30-minute, research mid-water trawl tows (primarily from F.H.C. Taylor et al. G.B. Reed 1963-1985 cruises, A.P. Knight 1971 cruises, supporting chartered, commercial vessels and W.E Ricker 1986-1999 cruises).

Red crosses indicate trawl tows where no eulachon were captured. Numerous exploratory trawl tows from other research cruises where no (or negligible) eulachon were captured are not plotted on the map. Eulachon catches (most < 850 kg) were frequently recorded between the 80-180 m bottom depth contour or along the edges of offshore banks (e.g. SE edge of the Goose Island Bank and the northern edge of Cook Bank in Queen Charlotte Sound, Two Peaks, Butterworth edge, Whiterocks, Bonilla and Horseshoe trawling grounds in Hecate Strait) and in the basins and gullies (e.g. Moresby and Mitchell's Gully) between offshore banks. Most eulachon were captured when mid-water trawl nets (e.g. Engel, Diamond #5, #7 & #8's) were fishing close to the sea floor and targeting on Pacific herring. Juvenile eulachon were also captured in shallower, inshore areas (e.g. Barkley Sound and Quatsino Inlet). Largest eulachon catches occurred off the lower, west coast of Vancouver Island (Maximum = 2,679 kg/hr on July 26, 1968), primarily around the perimeter edges of La Perouse Bank (Figure 3). Notice the absence of eulachon catches in the central, Strait of Georgia basin in the vicinity of the most highly ranked, herring spawning beaches of BC. Beach-spawning, capelin were frequently observed (e.g. Departure Bay, Lantzville, Denman Island and Ladner beaches) in the fall (first week of October) by local residents in this same central, Strait of Georgia region from the 1930's to the 1960's but as the presence of herring spawners increased in the central Strait of Georgia in the mid-1970's, these capelin spawners disappeared and spring-spawning, capelin became more evident in the Johnstone Strait and Central Coast regions of BC. Smaller catches of eulachon occurred in the Fraser River plume and southern Gulf Islands. Eulachon that are shown in Juan de Fuca Strait were trawled during fall and winter herring hydro-acoustic surveys in the 1970's when large schools of mid-water fish (e.g. herring, dogfish, hake and eulachon) were highly mobile and migrating along the strait. Each fishing location (center of circle) was plotted using SYSTAT software where the areas of circles were set proportional to catches (kg).


eulachon length frequencies

Graphs

Graphs

Graphs

Figure 5. Length frequency (L-F) histograms of juvenile eulachon measured off the central coast of British Columbia during the last three weeks of May from 1999-2013, 2016.

The surveyed areas where L-F samples were collected comprise the summer feeding grounds of eulachon and many other pelagic and bottom fishes concentrated near the productive banks (e.g. Goose Island, Cape Scott & Pearl Rock offshore trawling grounds) in Queen Charlotte Sound. Typical bimodal distributions correspond predominantly to age 1+ (60-130 mm) and age 2+ (100-180 mm) juvenile eulachon and also may include some age 3+ (140-200 mm) and older fish shown on the right tail of the curve. Age 0+ fish were under-represented in these samples because young-of-the-year (YOY) were either, not yet present on the offshore grounds (these areas were surveyed primarily during the last 3 weeks of May) or they were too small and fragile to be captured intact in a shrimp trawl net. Central coast eulachon spawn primarily from mid-March to mid-April in the lower reaches of glacier-fed rivers (e.g. Homathko, Klinaklini, Franklin, Kingcome, Nekite, Wannock/Oweekeno, Chuckwalla/Kilbella, Clyak, Quatna, Quatlena, Noeick/Taleomy/Asseek, Bella Coola/Paisla, Skowquiltz, Dean and Kimsquit). Eulachon larvae 5-6 mm in size are immediately flushed into receiving coastal inlets beginning in mid-April. Larval retention and dispersal occurs in nearshore areas and coastal fjords well into mid-June and July where eulachon post-larvae grow and rear in low salinity, surface waters. Eulachon stock delineations have been investigated using life history, meristic (e.g. vertebrae counts), chemical and genetic traits. Various degrees of geographical separation and isolation are evident as eulachon populations appear to be adapted to each river-marine estuarine complex (clusters of adjacent, glacier-fed rivers and/or tributaries).

Small-mesh, shrimp trawl nets and consistent fishing protocols were employed for each of the annual, offshore shrimp surveys where juvenile eulachon L-F samples were collected. Notice the absence (or low proportions) of age 1+ juvenile eulachon in the plots of 2002, 2004 and 2005 central coast samples (unimodal distributions of age 2+ and older individuals). Standard lengths (tip of snout to hypural plate) were measured to the nearest millimetre (mm) and pooled by 2 mm groupings on the histograms. Investigate offshore Central Coast-rearing, juveniles (1995 to 2013) and possible relationships with ocean conditions. - B. McCarter