Shark News - The WA Shark Cull Update

Since The WA Government announced their plans to set drum lines to catch sharks, the shark cull has been strongly opposed by members of the public, the scientific community and even some celebrities. The Department of Fisheries, WA seems to have conflicting views on the policy. On the one hand they promote the cull on their webpage, on the other they state quite clearly:

"Despite their sometimes-menacing appearance and 'man-eating' reputation, sharks seldom cause harm when interacting with humans. The presence of some shark species as ‘apex predators' – occupying the very top level of the food web – is actually an indication of a healthy marine environment."

For a while, the hopes of all opposed to the WA shark cull hinged on the indication that the Environmental Protection Authoriy (EPA) of WA would assess the shark cull and potentially overturn the policy. However, on the 12th March the EPA announced that they would not assess the shark cull as they believed the cull was not likely to significantly impact the environment.   

Since the cull began over 100 sharks have been caught. The policy of the government is to release any shark smaller than 3m and to destroy any shark which is one of the 3 target species and over 3m long; so far over 30 sharks being destroyed and 14 found dead on the line. The species which has been caught with an overwhelming frequency is the tiger shark (Galeocerdo cuvier).  

A female tiger shark which was destroyed as part of the policy. Photo credit: Bruce the Rib, Sea Shepherd  (c) Jodi Hayes 

In a recent press release, fisheries minister Ken Baston stated: "“We have caught and destroyed a number of large sharks within one kilometre of selected beaches, at a time of year when our beaches are crowded. This catch data proves there are a large number of big sharks near these beaches". He also commended the program, saying that the methods were "working well". 

This cull has brought to light the fact that large, tiger sharks frequent the inshore waters around WA and some of the most popular beaches...yet according to the Australian Shark Attack File there was only a single fatality from shark attacks in WA in 2013, and 2 in the previous year. Whilst any loss of life is an incredibly tragic event, it is hard to imagine that these low numbers really warrant such an expensive, controversial and damaging policy as the one Colin Barnett has implemented in WA with his shark cull.  

However, there could be hope for the future. There is a limit on how long the drum lines may remain in the water and the EPA has stated they expected that "a continuation of the proposal beyond April 30 2014 would be referred for consideration". 

Shark research: Spiny dogfish like their salt!

New research published in Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology has found that the North Pacific spiny dogfish (Squalus suckleyi) have difficulty adjusting to low salinity levels in the water.

The North Pacific spiny dogfish is known to tolerate a narrow range of salinities; whilst this species has been found in salinities of less than 25‰ in the wild, this low salinity cannot be tolerated for long. This is in contrast to certain other elasmobranch species such as the blue shark (Prionace glauca) which has been known to infiltrate river systems for extended periods of time.

Elasmobranch species moving between salt water and fresh water can experience changes in the concentration of Na^+, Cl^- and urea in their plasma, the pH of their blood and the volume of body water as they attempt to readjust to their new environment.

In this study, the researchers exposed S. suckleyi to dilute saltwater at a salinity of 21‰, in order to assess the time taken to acclimatise and the physiological effects this hyposmotic solution had.

They found that the concentration of plasma Na⁺, Cl^- and urea dropped, and the body weight of the experimental animals increased - most likely owing to an influx of water. Whilst S. suckleyi was able to begin to balance the Na⁺ and Cl^- concentrations, possibly by active transport, steady states in the concentration of plasma urea was not achieved and it is hypothesised that this is the key limiting factor for the survival of the North Pacific spiny dogfish in low saline environments.

Whilst it appears as though this species can tolerate an environment of 21‰ for a short period of time, the ability to regulate key body processed in a lowered salt environment would appear to restrict the long term survival of this species in water of this salinity.

Samuel C. Guffey, Greg G. Goss, Time course of the acute response of the North Pacific spiny dogfish shark (Squalus suckleyi) to low salinity. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. Volume 171, May 2014, Pages 9-15.

Shark research - Egg Capsule Evolution

An international team of researchers have constructed a phylogeny of chondrichthyan egg capsules by examining their morphological traits.

Chondrichthyan fish have cartilaginous skeletons - in contrast to osteichthyan (bony) fish - and comprise the Elasmobranchii (sharks, skates and rays) and the Holocephali (chimaeras). Whilst vivparity (giving birth to live young) dominates as the reproductive strategy in modern day Elasmobranchs, the Holocephali are exclusively oviparous (egg layers). The authors suggest that oviparity is the likely ancestral state for cartilaginous fish, whilst viviparity is assumed to have evolved several times in the Chondrichthyan lineage.

Chondrichthyan egg capsules are currently categorised into 10 morphotypes, with 8 of these types known from the fossil record. Using cladistical analysis of morphological traits of the egg capsules, the researchers attempted to see if the relationship would yield a phylogenetic signal.

They found that a very strong Elasmobranch group was generated, with very clear morphological similarities in the egg cases of Heterodontus, Orectolobus, Scyliorhinid and Rajoidae. The Holocephalan egg cases showed a greater similarity to the egg cases of extinct species than modern day Elasmobranchs.

The results suggest that the Elasmobranch egg capsule is the derived state and the ancestral reproductive state in both live bearing and egg laying jawed vertebrates is internal fertilization paired with clasper organs.

Jan Fischer, Martin Licht, Jürgen Kriwet, Jörg W. Schneider, Michael Buchwitz & Peter Bartsch (2014) Egg capsule morphology provides new information about the interrelationships of chondrichthyan fishes, Journal of Systematic Palaeontology, 12:3, 389-399,

Shark news - the truth about shark nets

The recent controversy regarding the shark cull in Western Australia has got a lot of people talking about the ways in which governments choose to protect their beaches from sharks - usually in the form of drumlines and shark nets. Several people I know have expressed surprise about the fact that shark nets are intended to kill sharks - there seems to be a public perception that netting a beach is a benign practice which simply keeps sharks away from the shore. In fact, shark nets are designed to kill large fish and mammals which become entangled and eventually drown.

Owing to the fact that shark nets are a non-discriminatory fishing process, it is not only sharks which are caught up; the nets trap many other species which swim too close and become entangled - this is known as bycatch. Dolphins, dugongs, turtles and whales are some of the species known to be caught up in shark nets (1, 2).

There is a great deal of controversy of whether or not netting a beach has any effect on reducing shark attack numbers. The construction of the nets does allow animals to swim below and around and some shark net programs have found a large degree of the entangled sharks to actually be on the beach side of the net! (3)

In Australia, shark nets have been in place along the Queensland coast as part of the Government's Shark Control Program (SCP) since 1962. In the last 10 years 6,252 sharks have been caught as a part of this program, over a third of which were tiger sharks (Galeocerdo cuvier) (4). The remaining numbers are made up of another 36 species of shark, 22 of which are grey nurse sharks (Carcharias taurus). Also known as the ragged tooth shark, C. taurus is a common aquarium shark and a popular shark to dive with owing to its placid nature.

Of more concern are the number of endangered species which are killed by shark nets - the SCP reported catching many species listed as Vulnerable in the IUCN Red List such as the grey nurse shark, the shortfin mako (Isurus oxyrinchus) and the whale shark (Rhincodon typus) (5). Most shark species exhibit slow growth rates and tend to take a long time to reach maturity, which means that once their numbers are depleted it is difficult for them to rebuild the population.  

The New South Wales (NSW) Shark Meshing Program (SMP) reported "72 interactions" with non-target species, vs. only "32 interactions" with target species. The non-target species included entanglement by Port Jackson Sharks (Heterodontus portusjacksoni), Southern Eagle Rays (Myliobatis australis) and 2 species of turtle (6). Two humpback whales were also entanglesd and whilst they swam away, they remained entangled as they swam and thus their survival is by no means assured.

Like all shark net projects, the NSW SMP is under scrutiny to perform in an ecological manner and to reduce bycatch numbers, and they do implement certain methods to attempt to reduce interactions with non-target species - for example the shark nets are removed for the whale migratory seasons from May to August. However, the fact remains that shark net programs are responsible for the death of a great many species of sharks, marine mammals and reptiles and are acting in response to a threat which is more perceived than real. In 2013, 10 people died globally from shark attacks (7) vs. an estimated 388,000 deaths from drowning worldwide annually and - the biggie - approximately 1.24 million annual deaths from road traffic accidents (8). It just seems as though the money and time of any government could be better invested in tackling the real dangers which exist in society, instead of using methods which are incredibly destructive to the marine environment in order to simply make people feel better about going in the water.

1. Qld's Fisheries Department defends shark nets amid trapped whale worries
2. Dolphin deaths a tragic find for local kayakers
3. Fisheries Scientific Committee
4. Department of Agriculture, Fisheries & Forestry - Shark Catch Numbers
5. IUCN Red List
6. Shark Meshing (Bather Protection) Program 2012-13 Annual Performance Report
7. International Shark Attack File (ISAF)
8. World Health Organisation - Factsheet - Drowning

Shark Research - Researchers in Brazil find new techniques to improve the survival rate of tiger sharks caught in longline fisheries

Researchers in Brazil have used tagging methods to study the mortality and behaviour of juvenile tiger sharks (Galeocerdo cuvier) after they had been caught and released from bottom longline fishing gear.

The researchers tagged 21 tiger sharks caught in longlines during the course of the experiment. The sharks were hooked by the jaw using circle hooks as oppose to J-hooks - a method which has been previously proven to improve survival rates post-release. After the sharks were released, their movements were monitored via satellite. Most of the sharks caught were released in good health and none of the individuals died within 30 days of release, indicating that this species could be robust enough to successfully survive catch and release from longline circle hooks when caught as bycatch. This could be particularly important in this region of Brazil owing to the fact that all the sharks caught in this study were juveniles and therefore had no opportunity to reproduce. The authors also noted that the fishing pressure on the local shark population in this region was particularly high as artisanal fishermen in neighbouring waters fishing with gillnets and reported a much higher mortality rate for tiger sharks than reported from this study using longline circle hooks.

Interestingly, the researchers also discovered that tiger sharks released after capture tended to move into deeper water and did not return to the same area where they were captured for a considerable time. This suggests that these catch and release methods could be employed to successfully relocate problem tiger sharks in the area - a strategy which would be preferable to culling.

Other studies have predicted that tiger sharks are a keystone species in many ecosystems, and the removal of this apex predator would cause a great deal of disturbance in the ecosystems they are associated with. Therefore effective management strategies to minimise the impact of the fishing industry on tiger sharks are essential.  

Sharks, along with other marine animals, are often caught unintentionally by the fishing industry as bycatch and estimates suggest that the bulk of this is ascribed to longline fisheries. The fact that tiger sharks could survive catch and release - at least if circle hooks are used for the capture - could be used to facilitate the effective management of longline fisheries with regards to shark conservation.

André S. Afonso, Fábio H.V. Hazin, Post-release survival and behavior and exposure to fisheries in juvenile tiger sharks, Galeocerdo cuvier, from the South Atlantic, Journal of Experimental Marine Biology and Ecology, Volume 454, May 2014, Pages 55-62
Link to the paper

Other posts related to this one:

Brazil looks at better ways of keeping beaches safe

Shark Research: Public perceptions of shark conservation

New research has conducted a survey on aquarium goers to assess the views of the public on sharks and their conservation.

The survey, published in the journal Marine Policy, posed a series of questions related to shark conservation to the visitors of the National Marine Aquarium in Plymouth. The questions focused on assessing the respondents general knowledge of sharks as well as their knowledge of shark fisheries. Whilst nearly all survey participants displayed a good general knowledge of sharks, there was a large degree of uncertainty when questioned about shark fisheries with 21% of respondents incorrectly believing that sharks were not fished in European waters and 19% answering (incorrectly) that shark meat was not consumed in the UK.

The participants were also interviewed regarding their perception of sharks. Approximately two thirds of the survey group had a positive image of sharks and individuals who had encountered sharks in the wild displayed a more positive attitude towards sharks.

Public perception of sharks could be an important factor influencing shark conservation. When people hold high views of wild animals, they have a tendency to participate in activities to promote the protection of those animals and to avoid products and practices which could be detrimental to the survival of that species in the wild. Public opinion can be a strong driving force for policy making and bolstering protection for certain animals; a well informed and motivated public may hold the ability to drive change in terms of shark conservation.

Sharks are under threat globally owing to the pressure exerted on many species from shark finning and fishing bycatch and the study states that around half of sharks in European waters are at risk of becoming endangered or threatened with extinction. Low fecundity, slow growth rates and length of time taken to reach maturity mean that most shark species do not rebound easily once their numbers have been depleted. Finding more ways to drive public perception of sharks and to motivate individuals to become involved with shark conservation could be a real driving force for preventing the decline of these vulnerable species.  

Shark Research: Population composition of blue sharks in the Central Atlantic

A group of researchers has examined population structure, size, abundance and migration patterns of blue sharks (Prinace glauca) in the Azores Archipelago in the Central North Atlantic.

Unlike many other shark species, blue sharks are relatively productive and may attain high abundances locally. This is reflected in the fisheries catch composition which the researchers monitored in the local area where blue sharks constituted 81.5% of the total catch in terms of number of individuals caught.  

Blue shark composition varies with sea surface temperature (SST), time of year and lunar cycle. The highest catch rate of blue sharks in the Central North Atlantic occurred during the winter months whilst the summer months yielded the lowest catch rate. This is congruent with evidence that female blue sharks migrate in the warmer months and appear off the coasts of Ireland and SW England. The highest catch abundance of blue sharks also coincided with the coolest SSTs, with the highest catch rate occurring in waters of 17.5°C and the lowest at the higher SST of 23°C. Evidence of several life stages of the blue shark in the Central North Atlantic indicates that this is an important ecological area for blue shark populations from both sides of the North Atlantic, as well as being a nursery area for blue sharks.

Owing to the over exploitation of many shark species by the fisheries industry, in depth knowledge of population structure and composition of shark species is an important tool in assessing vulnerability of each species. The blue shark is the most frequently caught pelagic shark species by the fisheries industry, with an estimated 86,000 tonnes fished per year; in recent years the swordfish fisheries have begun to target blue sharks owing to a reduction in the swordfish catch in the region.

Vandeperre, F., Aires-da-Silva, A., Santos, M., Ferreira, R., Bolten, A. B., Serrao Santos, R. and Afonso, P. (2014) Demography and ecology of blue shark (Prionace glauca) in the central North Atlantic. Fisheries Research. 153, 89-102