MY DEEP SEA MSC RESEARCH AND WHY DEEP SEA FISHERIES OVERSIGHT IS NEEDED
“You’re not what I expected when you said you were a shark scientist.” Gee, thanks. I can’t tell you how many times I’ve heard that I don’t live up to someone’s preconceived mental image of what I should look like as a “shark scientist.” It doesn’t change the fact that I’m a marine biologist though, and that I am very passionate about my field.
I recently wrapped up my Masters in Marine Biology, focusing on “Habitat use throughout a Chondrichthyan’s life.” Chondrichthyans (class Chondrichthyes) are sharks, skates, rays, and chimaeras. Today, there are more than 500 species of sharks and about 500 species of rays known, with many more being discovered every year.
Over the last few decades, much effort has been devoted towards evaluating and reducing bycatch (the part of a fishery’s catch that is made up of non-target species) in marine fisheries. There has been a particular focus on quantifying the risk to Chondrichthyans, primarily because of their high vulnerability to overfishing. My study focused on five species of deep sea chimaeras (not the mythical Greek ones, but the just-as-mysterious real animal) found in New Zealand waters:
• Callorhynchus milii (elephant fish),
• Hydrolagus novaezealandiae (dark ghost shark),
• Hydrolagus bemisi (pale ghost shark),
• Harriotta raleighana (Pacific longnose chimaera),
• Rhinochimaera pacifica (Pacific spookfish).
These species were chosen because they cover a large range of depth (7 m – 1306 m), and had been noted as being abundant despite extensive fisheries in their presumed habitats; they were also of special interest to the Deepwater Group (who funded the scholarship for my MSc).
Although there is no set definition for what constitutes as “deep sea,” it is conventionally regarded to be >200 m depth and beyond the continental shelf break (Thistle, 2003); in this zone, a number of species are considered to have low productivity, leading to them having a highly vulnerable target of commercial fishing (FAO, 2009). Deep sea fisheries have become increasingly economically important over the past few years as numerous commercial fisheries become overexploited (Koslow et al., 2000; Clark et al., 2007; Pitcher et al., 2010). Major commercial fisheries exist for deep sea species such as orange roughy (Hoplostethus atlanticus), oreos (several species of the family Oreosomatidae), cardinalfish, grenadiers (such as Coryphaenoides rupestris) and alfonsino (Beryx splendens). Many of these deep sea fisheries were not sustainable (Clark, 2009; Pitcher et al., 2010; Norse et al., 2012) with most of the stocks having undergone substantial declines.
Deep sea fishing can also cause environmental harm (Koslow et al., 2001; Hall-Spencer et al., 2002; Waller et al., 2007; Althaus et al., 2009; Clark and Rowden, 2009). Deep sea fisheries use various types of gear that can leader to lasting scars: bottom otter trawls, bottom longlines, deep midwater trawls, sink/anchor gillnets, pots and traps, and more. While none of this gear is solely used in deep sea fisheries, all of them catch animals indiscriminately and can also damage important habitats (such as centuries-old deep sea coral). In fact, orange roughy trawling scars on soft-sediment areas were still visible five years after all fishing stopped in certain areas off New Zealand (Clark et al ., 2010a).
Risk assessment is evaluating the distributional overlap of the fish with the fisheries, where fish distribution is influenced by habitat use. For sharks, that risk assessment included a lot of variables: there are a number of shark species (approximately 112 species of sharks have been recorded from New Zealand waters) with many different lifestyles, differences in their market value for different body parts (like meat, oil, fins, cartilage), what body parts they use for sharks (for example, some sharks have both their fins and meat utilised but not their oil; some just have their fins taken, etc.) and how to identify sharks once on the market (Fisheries Agency of Japan, 1999; Vannuccini, 1999; Yeung et al. 2000; Froese and Pauly, 2002; Clarke and Mosqueira, 2002).
In order to carry out a risk assessment, you have to know your study animals pretty well. It should come to no surprise that little is known about the different life history stages of chimaeras, so I did the next best thing and looked at Chondrichthyans in general. My literature review synthesized over 300 published observations of habitat use for these different life history stages; from there, I used New Zealand research vessel catch data (provided by NIWA, the National Institute of Water and Atmospheric Research) and separated them by species, sex, size, and maturity (when available). I then dove into the deep end of using a computer language called “R,” which is used for statistical computing and graphics. Using R programming software, I searched for the catch compositions based on the life history stage I was looking for (example: looking for smaller sized, immature fish of both sexes and little to no adults when in search for a nursery ground).
The way we went about this thesis differs in that we first developed hypotheses for characteristics of different habitat use, rather than “data mining” for patterns, and it therefore it has a structured and scientific approach to determining shark habitats. Our results showed that some life history stages and habitats for certain species could be identified, whereas others could not.
Pupping ground criteria were met for Callorhynchus milii (elephant fish), Hydrolagus novaezealandiae (dark ghost shark), and Hydrolagus bemisi (pale ghost shark); nursery ground criteria were met for Callorhynchus milii (elephant fish); mating ground criteria were met for Callorhynchus milii (elephant fish), Hydrolagus novaezealandiae (dark ghost shark), Hydrolagus bemisi (pale ghost shark), and Harriotta raleighana (Pacific longnose chimaera); lek-like mating criteria were met for Hydrolagus novaezealandiae (dark ghost shark). Note: Lek-like mating is where males perform feats of physical endurance to impress females and she gets to choose a mate.
These complex—and barely understood— deep sea ecosystems can be overwhelmed by the fishing technologies that rip through them. Like sharks, many deep sea animals live a k-style lifestyle, meaning that they take a long time to reach sexual maturity and once they are sexually active, they give birth to few young after a long gestation period. This lifestyle means these creatures are especially vulnerable since they cannot repopulate quickly if overfished.
In order to manage the environmental impact of deep sea fisheries, scientists, policymakers and stakeholders have to identify the ways to help re-establish delicate biological functions after the impacts made by deep sea fisheries. Recovery—defined as the return to conditions before they were damaged by fishing activities—is not a unique concept to just deep sea communities, and is usually due to site-specific factors that are often poorly understood and difficult to estimate. Little is known about biological histories and structures of the deep sea, and therefore the rates of recovery may be much slower than shallow environments.
Management of the seas, especially the deep sea, lags behind that of land and of the continental shelf, but there is a number of protection measures already being put in place. These actions include, but are not limited to,
• regulating fishing methods and gear types,
• specify the depth that one can fish at,
• limit the volume of bycatch, limit the volume of catch,
• move-on rules, and
• closure of areas of particular importance.
Modifications to trawl gear and how they are used have made these usually heavy tools less destructive (Mounsey and Prado, 1997; Valdemarsen et al. 2007; Rose et al. 2010; Skaar and Vold 2010). Fishery closures are becoming more common, with large parts of EEZs (exclusive economic zone) being closed zones for bottom trawling (e.g. New Zealand, North Atlantic, Gulf of Alaska, Bering Sea, USA waters, Azores) (Hourigan, 2009; Morato et al. 2010); the effectiveness of these closures is yet to be established.
And while this approach, dubbed the “ecosystem approach,” to fisheries management is widely advocated for, it does not help every deep sea animal or structure. Those that cannot move (sessile) are still in danger of being destroyed. As such, ecosystem-based marine spatial planning and management may be the most effective fisheries management strategy for protecting the vulnerable deep sea critters (Clark and Dunn, 2012; Schlacher et al. 2014). This management strategy can include marine protected areas (MPAs) to restrict fishing in specific locations and other management tools, such as zoning or spatial user rights, which will affect the distribution of fishing effort in a more effective manner. Using spatial management measures effectively requires new models and data, and will always have their limitations given how little data in regards to the deep sea exists, and that this particular environment is hard to get to.
So what does it all mean in regards to my thesis? Well, for one thing, there is a growing acknowledgement these unique ecosystems require special protection. And like any scientist knows, there are still many unanswered questions about just how important this environment is (especially certain structures).
On a more shark-related note, not all life-history stage habitats were found for my chimaeras, and this may be because these are outside of the coverage of the data set (and likely also commercial fisheries), or because they do not actually exist for some Chondrichthyans. That cliffhanger is research for another day, I suppose…
This project could not have been done without the endless amount of support of my family and friends; those who have supported me since day one of my marine biology adventures. They’re the ones who stick up for me whenever I hear, “You’re not what I expected when you said you were a shark scientist.” I am not really sure what the stereotype of a shark scientist is supposed to be, thankfully I grew up where you accept and judge people by who they are and what they do. However I see this as a challenge, as it sets the stage up for me to show the mind of a shark scientist can come in all kinds of packages.
As a final note, I’d like to thank the New Zealand Seafood Scholarship, the Deepwater Group, as well as researchers from National Institute of Water and Atmospheric Research (NIWA) who provided funding, insight and expertise that greatly assisted the research. The challenge of venturing into complex theories is that not all agree with all of the interpretations/conclusions of any research, but it is a basis for having a discussion, which can only be good for all.
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