Management Plan for the Bluntnose Sixgill Shark and Tope Shark in Canada [Proposed] 2012: Threats

The Bluntnose Sixgill Shark and the Tope Shark are threatened by various anthropogenic sources. Five classes of current threats have been identified in this Management Plan, which are entanglement/bycatch, pollution, habitat loss or degradation, climate and oceanographic change, and harassment. Historic threats included directed fisheries and entanglement/bycatch. The influence of some or all of these current threats may affect normal behaviour, habitat use, or result in direct mortality. In the Northeast Pacific ocean, the Bluntnose Sixgill Shark is found from Alaska, U.S., down through Baja California, Mexico. The Tope Shark is found from northern British Columbia, to Baja California including the Gulf of California, Mexico. However, the extent of individual migration throughout the distribution range is currently unknown. These are highly mobile sharks, so there is a possibility of transboundary exchange. The cumulative effect of any combination of these threats listed below in the threat classification table (Table 1), in conjunction with species-specific limiting factors (see Section 1.6 ‘Limiting Factors’), may result in more serious consequences than those of any single threat acting upon the population in isolation.

Assessment of threats to both the Bluntnose Sixgill Shark and Tope Shark (Table 1) allows for the prioritization of recommended management and other actions to prevent these species from becoming threatened or endangered. The following threats have been identified for both species and ranked in terms of significance, with the greatest threat to the survival of the species appearing at the top of the table. Current and historic threats have been identified under separate headings. It is to be noted that only current threats were ranked. Historical threats are identified due to the impact on the population, but have not been included in the ranking system as they currently have no level of concern to the present population. Description of each current and historic threat is provided in the section following the table. Threats identified in this table are specific to Canadian Pacific waters only; however, it can be assumed that these threats are relevant in the U.S. and Mexico components of each species range. Threats outside of Canada, such as the recreational fishery for Tope in California, have not been included here. Definitions of the terms used for ranking are available in Appendix III.

Current Threats

The only threat identified in the COSEWIC Assessment Reports (2007a, 2007b) to both the Bluntnose Sixgill Shark and the Tope Shark was fishing. This threat is here classified as ‘entanglement/bycatch’. The Technical Team identified four additional current threats, which include pollution, climate and oceanographic change and harassment, habitat loss or degradation. While these populations are migratory throughout the northeast Pacific, it is unknown whether threats occurring outside of Canadian Pacific waters have an impact on these populations. For example, commercial landings of Tope Shark in California averaged approximately 150 tonnes annually from 1990-1999; however, no data exists for landings from recreational fisheries (Ebert 2001). It is unknown whether this level of removal has any impact on the Tope population within Canadian Pacific waters. All five current threats to the Bluntnose Sixgill Shark and Tope Shark within Canadian Pacific waters are discussed in further detail below.

Entanglement/Bycatch

Fishing activities are the primary threats to the Bluntnose Sixgill Shark and the Tope Shark. Currently, the only directed shark fishery in Canadian Pacific waters is for Pacific Dogfish (Squalus acanthias). Both the Bluntnose Sixgill Shark and the Tope Shark are incidentally caught in other fisheries, particularly the groundfish trawl and groundfish hook and line fisheries (Tables 2-5). Commencing with the 2011/2012 season, no commercial fishery in Canadian Pacific waters is permitted to retain Bluntnose Sixgill or Tope Shark; all bycatch for these species is to be released at sea with the least possible harm. The level of bycatch and entanglement of Bluntnose Sixgill Shark and Tope Shark in Aboriginal fisheries and aquaculture is unknown.

Commercial Groundfish Trawl Fisheries

The commercial groundfish trawl fleet has been monitored with 100% at-sea observer¹ coverage since 1996. Prior to 2001, reporting of non-commercial elasmobranch species was incomplete in this fishery (COSEWIC 2007a). Between 2001 and 2009, a total of 6.2 t of Bluntnose Sixgill Shark was reported as bycatch, which equates to approximately 0.7 t/yr. The number of Bluntnose Sixgill Shark this represents is unknown; however, if we assume an average size of 40 kg, as observed in trawl bycatch since 2001 (PacHarvTrawl and GFFOS databases), then 19 Bluntnose Sixgill Shark per year are possibly being caught by trawl gear (Table 2). Since 2001, approximately 63% of the total catch has occurred within Pacific Marine Fisheries Commission (PMFC) areas 3C/D (west coast of Vancouver Island) and 4B (Strait of Georgia). See Appendix IV for a map of PMFC areas.

* from fisherman logbook
† from a dockside observer validation
‡ from both fisherman logbooks and dockside observer validations
Source: PacHarvTrawl and GFFOS fisheries databases.
All data are from observer logbooks, unless otherwise noted. Data prior to 2001 is considered incomplete and not included in average. Number of sharks is estimated by assuming an average weight of 40 kg.

Between 2001 and 2009, a total of 4.4 t of Tope Shark has been incidentally caught by British Columbia trawl fisheries, which equates to approximately 0.48 t/yr. Assuming an average weight of 21 kg, as observed in trawl bycatch since 2001 (COSEWIC 2007b), it is estimated that 23 Tope Shark per year are caught by the trawl fleet. Most of the catch is from PMFC areas 3C/D (Table 3).

Source: PacHarvTrawl and GFFOS fisheries databases.
Data prior to 2001 is considered incomplete and not included in average. Estimated number of sharks based on mean weight of 21 kg.

Commercial Groundfish Hook and Line Fisheries

Hook and line groundfish fisheries, including fisheries for Pacific Dogfish, Lingcod, Rockfish, Halibut and Sablefish, have only recently (since 1999) been subject to at-sea observers. Since 2006 all vessels have been required to have 100% at-sea observer coverage either in the form of electronic monitoring or an at-sea observer. From 2001 to 2005, coverage was between 10-15% per fleet (DFO 2003, 2004, 2005). In addition, some fishers reported Bluntnose Sixgill Shark and Tope Shark catches in logbooks (Tables 4,5). Fishers are obligated to report catches of shark in their logbooks; however, sufficient monitoring could not verify accuracy and thus, the actual amount caught is estimated to be higher. Therefore, we expanded the estimates presented for 2001 to 2005 to 100% assuming 10% observer coverage during those years (Tables 4, 5). Using this expanded estimate, an average of 21.5 t of Bluntnose Sixgill Shark was caught annually (Table 4). Using an estimate of 60 kg average weight, as observed in the hook and line fisheries since 2001 (PacHarvHL and GFFOS databases), 359 Bluntnose Sixgill Shark could be captured annually by hook and line fisheries.

Source: PacHarvHL and GFFOS fisheries databases.
* starting April 2006, all hook and line vessels subject to 100% at-sea observer coverage in the form of electronic monitoring or at-sea observers.
From 2001-2005, estimated number of sharks based on a mean weight of 60 kg. Total catch weight and number of sharks in parentheses represent extended values, from 10% to 100% observer coverage. From 2006-2009, fisherman logbooks recorded counts (or number of sharks). A catch weight for each year was calculated by multiplying the number of sharks caught by an average weight of 60 kg, except where specified. Source: PacHarvHL and GFFOS fisheries databases.

A total of 15.1 t of Tope Shark was captured by hook and line fleets (Table 5) between 2001 and 2009, which equates to 1.7 t annually, based on expanded observer and logbook records. Using an estimate of 27 kg average weight, as observed in the hook and line fishery since 2001 (PacHarvHL and GFFOS databases), 62 Tope Shark could be incidentally caught annually by hook and line fisheries.

Source: PacHarvHL and GFFOS fisheries databases.
From 2001-2005, estimated number of sharks based on a mean weight of 27 kg. Total catch weight and number of sharks in parentheses represent extended values, from 10% to 100% observer coverage. From 2006-2009, fisherman logbooks recorded counts (number of sharks). A catch weight for each year was calculated by multiplying the number of sharks caught by an average weight of 27 kg, accept where specified.
* starting April 2006, all hook and line vessels subject to 100% at-sea electronic monitoring.
** estimated catch weight a combination of at-sea observer weight (n = 1) and estimated weight from fisherman logbook (n = 1)
*** catch weight from at-sea observer.
† values are very high and are likely indicative of species misidentification.

A combined total of 21.7 t of Bluntnose Sixgill Shark (approximately 377 sharks) and 2.2 t of Tope Shark (approximately 85 sharks) are incidentally caught in groundfish trawl and groundfish hook and line fisheries annually. Mortality associated with this bycatch has not been investigated; however, many sharks are reported as “released alive”. According to one Pacific Dogfish harvester, Bluntnose Sixgill Shark captured on longlines are usually lively at the surface and swim away when released (COSEWIC 2007a). The impact of this catch on the population depends on the size of the population which at present time is unknown for these species. At current minimum estimates of biomass for the west coast of North America (a minimum of 7,900 individuals of Bluntnose Sixgill Shark and 1,500 t of Tope Shark), it is unlikely present mortality levels are having a significant impact on the populations. This threat is considered to be a “medium” level of concern.

Pollution

The threat of pollution to the Bluntnose Sixgill Shark and Tope Shark could originate from petroleum spills from oil tankers, drill rigs, or ocean-going vessels; waste from ocean-going vessels; or biological contaminants via sewage outflow or industry discharge. Spills are recurrent events along the BC coast, and the likelihood of accidental spills may increase with high densities of traffic or increased shoreline development. The subsequent decrease in water quality in the pelagic zone from spills or introduction of biological pollutants could result in increased mortality of Tope Shark and newborn or juvenile Bluntnose Sixgill Shark both directly and indirectly through a decline in prey availability. Biological contaminants accumulate in marine food webs, and magnification of these contaminants increase with increasing position in the food web. Given that both these species are apex predators, bioaccumulation of contaminants (from sewage outflow or industry discharge) may also be a concern, particularly for juveniles if they retain these contaminants and accumulate throughout their lifespan. No contaminant studies have been done on Bluntnose Sixgill Shark or Tope Shark; however, levels of persistent contaminants in other apex predators have been associated with health effects such as reproductive impairment, skeletal deformities, and suppression of the immune system (DFO 2009, 2010). While measures to prevent and mitigate effects of spills or discharge of biological contaminants are currently in place, success of these measures is highly dependent on proximity to population centers with facilities and expertise for cleanup. For example, once an oil spill occurs, the effectiveness of clean up measures is low (Graham 2004). As the threat of pollution is of unknown severity and low causal certainty, it is considered to be a “low” level of concern.

Habitat Loss or Degradation

A species’ survival is subject to the conditions in the zone it occupies at any particular life stage. As Tope sharks rarely occupy nearshore coastal waters such as bays and inlets in Canadian Pacific waters, this is likely not a threat for them. The main nursery area for Tope shark is the Southern California Bight, which is heavily industrialized (Ebert, pers. Comm. 2011.) However, these impacts are obviously beyond management efforts in Canadian waters The urbanization of coastal areas in British Columbia through the development of marinas, docks, ferry terminals, tanker ports, wind farms, log dumps, aquaculture sites and other similar installations may result in the physical exclusion of juvenile Bluntnose Sixgill Shark from their preferred shallower water habitats. In addition, these activities and related ancillary works could create localized water quality issues which may compromise prey availability. Thus, physical degradation of habitat may displace juvenile Bluntnose Sixgill Shark, affect their potential to feed, or affect reproductive success. Due to high uncertainty with respect to frequency and severity, the level of concern is considered to be “low”.

Climate and Oceanographic Change

Large scale climate change (decadal regime shifts, global warming) has been correlated with major step-like changes in zooplankton composition (Mackas et al. 2004) and fish (McFarlane et al. 2000, Beamish et al. 2008). Bluntnose Sixgill Shark and Tope Shark are known to feed on a variety of invertebrates and bony fishes which would be impacted by climate change. Impacts of climate change on these sharks may be limited to changes in food resources (e.g., abundance and distribution) and temperature, which would manifest themselves through changes in Bluntnose Sixgill Shark and Tope Shark distribution and growth. Little information is available on changes in shark distribution or other biological parameters in relation to prior decadal scale climate events. However, due to changing ocean productivity associated with climate change, it is likely these sharks, particularly Tope Shark and juvenile Bluntnose Sixgill Shark, would significantly change their distribution patterns following food resources. Also, given the affinity of females for specific water temperatures, and newborn pups and juveniles for shallow water rearing (COSEWIC 2007a, Andrews et al. 2007), a warming climate may induce a major shift in spawning or parturition areas and nursery grounds (King et al. 2011). Due to the high uncertainty with respect to the occurrence, frequency and severity of the threat of climate change, the level of concern is considered to be “low”.

Harassment

During the last few decades, a recreational SCUBA dive industry has developed in the Strait of Georgia and off the west coast of Vancouver Island, taking clients to dive with the Bluntnose Sixgill Shark. It is unknown whether these human-shark encounters impact normal behavior (i.e., feeding or nearshore residency times) of the Bluntnose Sixgill Shark, predominantly to the large juveniles. More recently, anecdotal reports have noted intentional feeding or baiting of Bluntnose Sixgill Shark to bring them to the surface for viewing, which could make them more susceptible to human impacts such as encounters with boats and fishing gears; however, it is to be noted that this is not a known practice in the dive industry. Further, the impacts of underwater noise through seismic, explosives, or otherwise on sharks in general has not been well documented. Overall, harassment is considered to be a “low” level of concern.

Historical Threats

Directed fishing

The Bluntnose Sixgill Shark has been the focus of at least three known directed fisheries in Canadian Pacific waters. The first fishery occurred in the early 1920s with a focus on their skins used to make shark leathers. The success of this venture in terms of sharks caught and duration is unknown .The second fishery took place between 1937 and 1946 with a focus on the shark livers for vitamin A. Between 1942 and 1946, 276 t of Bluntnose Sixgill Shark liver (approximately 3800 sharks) was marketed in British Columbia (COSEWIC 2007a). Similar liver-directed fisheries for Bluntnose Sixgill Shark occurred in adjacent Washington State waters during this time period (Bargmann pers. comm. 2006). The combined long-term effect of these fisheries on the northeast Pacific population has never been investigated. The third commercial fishery for the Bluntnose Sixgill Shark within Canadian Pacific waters commenced under an experimental basis in the late 1980s and again in 1994, but was terminated due to conservation concerns, particularly since the experimental fishery captured only juveniles (McFarlane et al. 2002).

The Tope Shark was the target of a brief but extensive commercial fishery throughout their northeast Pacific range beginning in 1937 in California and then in British Columbia, Oregon, and Washington in the early 1940s. This fishery targeted the Tope Shark primarily to extract for their liver, which contains the highest concentrations of vitamin A of any fish on the Pacific coast. A total of approximately 840,000 Tope Shark may have been taken from the northeast Pacific population; of this total, 50,000 were estimated to have landed in Canadian ports, although the amount actually caught in Canadian waters is unknown. The Canadian fishery took place primarily off the west coast of Vancouver Island and in Hecate Strait (COSEWIC 2007b). Canadian fishing magazines were reporting a decrease in Canadian abundance starting in 1944, and by 1946 the Canadian fishery had substantially diminished. Vitamin A was first synthesized in 1947, which removed the demand on natural sources for its procurement. By 1949, the Canadian fishery for Tope Shark had ended.

The intensive fishery for Tope Shark between 1937 and 1949 throughout their migratory range in the northeast Pacific caused depletion in the adult biomass (Walker 1999; Ebert 2003). Since that time, the Tope Shark has not received any commercial or research attention. The degree to which the stock has recovered since the 1940s is unknown. Walker (1999) argues that although the fishery collapsed during the 1940s, due to the manufacture of synthetic Vitamin A, it is unlikely the stock collapsed.

Entanglement

Little information exists on bycatch of Bluntnose Sixgill Shark and Tope Shark in the historic record as shark bycatch was not broken down by species. Although limited, the information that does exist indicates both species were caught in groundfish longline and to a lesser extent trawl fisheries. It is likely, given the lower effort levels in these fisheries compared to more recent fisheries, that bycatch levels would have been very low.

Internationally, the IUCN Red List has assessed the Bluntnose Sixgill Shark as ‘near threatened’ globally (Cook and Compagno 2005), and Tope Shark as ‘vulnerable’ globally and as ‘least concern’ in the northeast Pacific region (Walker et al. 2006). Bluntnose Sixgill Sharks are included under Annex 1 of the UN Convention on the Law of the Sea. Under the Inter-American Tropical Tuna Commission, of which Canada is a party, all sharks incidentally caught within IATTC fisheries must be reported, and released unharmed and alive with minimal harm, where practicable; and any landings of shark must use the full shark carcass (IATTC 2005).

Within Canada, as with all marine species, the Bluntnose Sixgill Shark and Tope Shark are federally protected under the Fisheries Act. Commencing with the 2011/2012 season, no commercial fishery in Canadian Pacific waters is permitted to retain Bluntnose Sixgill Shark and Tope Shark; all fisheries are required to release these species bycatch at sea with the least possible harm. Since 1996, the groundfish bottom trawl fishery has been monitored intensively (100% observer coverage on all trips); since 2006, all commercial hook and line/trap groundfish fisheries have 100% at-sea monitored in the form of observers or electronic monitoring. This monitoring, in addition to fishing logbooks, should allow for more accurate accounting of shark bycatch in these fisheries. Recreational shark fishing is managed under the finfish recreational fisheries. While Bluntnose Sixgill Shark have been protected from retention in the recreational fishery since 1996, a recent Variation Order to the BC Sport Fishing Regulations provided further conservation measures for shark species within the recreational fishery. As of April 1, 2011, catch limits will be reduced from 20 individuals per day to “no fishing” for all SARA-listed species (including Bluntnose Sixgill Shark and Tope Shark), and “zero retention” (catch and release) for all other shark species with the exception of Salmon Shark, which was reduced to a daily limit of one individual per day and a possession limit of two, and Spiny Dogfish, which was reduced to a daily limit of four individuals per day and a possession limit of eight. These measures are captured in the 2011-2013 BC Tidal Waters Sport Fishing Guide.

A “Sharks of British Columbia” Identification Guide was created in 2011 to increase proper identification and enhance awareness of shark species in Canadian Pacific waters. This guide was distributed to all groundfish commercial harvesters as part of their 2011/2012 licences, and is available for distribution to commercial and recreational harvesters as well as for communication and outreach purposes. Scientific research has been conducted for these species; however, numerous knowledge gaps exist (see section 1.7, “Knowledge Gaps”). A Bluntnose Sixgill Shark tagging survey was conducted in March 2011 to provide information on the seasonal distribution, movement, and migration in the Strait of Georgia. Eight Bluntnose Sixgill Sharks were tagged in this survey, results of which are anticipated to be available in Spring 2012. Further, information on genetic population stock structure does not currently exist for shark species that utilize Canadian Pacific waters. A genetic sampling program was implemented in spring 2011 to collect biological samples from scientific surveys as well as from incidentally caught species via the at-sea observer program. Additional funding past 2011 will be considered, as required.

Knowledge gaps for both the Bluntnose Sixgill Shark and the Tope Shark include information pertaining to the species’ abundance, current abundance trends, distribution, biology, ecology and threats. For example, information on biological parameters such as longevity, age at first maturity, fecundity and survival rates is limited and is vital to understanding factors that regulate population productivity. Information on pupping or nursery grounds throughout its range would help identify the nearshore residency times by juveniles and timing of subsequent migration to deepwater habitat. Information on genetic makeup within B.C. will foster an understanding of local and regional dispersal and will allow identification of stock structure to assist in the management of population level threats. The current effects of pollutants on both species are unknown (particularly pollutants resulting from atmospheric fallout) and vital given their apex predator status. This would assist in understanding the impact of this threat to both species. Further, more detailed information on diet requirements for both species and the seasonal abundance and distribution of prey may be important in identifying areas where future fisheries interactions may occur, and /or the impacts of climate change. While Bluntnose Sixgill Shark and Tope Shark are often “released live” when incidentally caught, actual mortality of these released sharks is unknown. Further, the level of bycatch and entanglement of Bluntnose Sixgill Shark and Tope Shark in Aboriginal fisheries and aquaculture is unknown.

¹As a condition of licence, all commercial groundfish vessels must have 100% at-sea monitoring. For hook and line and trap vessels, this may include either electronic monitoring or a third-party at-sea observer. For Option A trawl vessels (fishing outside of the Strait of Georgia), this includes a third-party at-sea observer; for Option B (fishing in the Strait of Georgia) and mid-water directed Pacific hake trawl vessels, this includes electronic monitoring.