Troutzilla wrote: ... I guess the question then is how deep is too deep to catch snapper from and release them - while still giving them a strong chance of survival. |
Capture depth related mortality of discarded snapper (Pagrus auratus) and implications for management
John Stewart New South Wales Department of Primary Industries, Cronulla Fisheries Research Centre of Excellence
Received 9 August 2007; received in revised form 31 October 2007; accepted 2 November 2007
...capture depth had the greatest affect on short-term survival of snapper, with no mortalities observed from depths of less than 21m and ∼2% from depths of less than 30 m. Mortality of snapper increased rapidly after 30m and was ∼39% between capture depths of 30 and 44m and ∼55% between capture depths of 45 and 59 m.
Survival was also effected by fish length, with smaller fish being more likely to die.
Capture depth has a major influence on survival of fish that are discarded and there is an inverse relationship between capture depth and survival (Rummer and Bennett, 2005; St. John and Syers
Capture depth had the greatest affect on survival of snapper (Table 4). There were no mortalities of snapper from capture depths less than 21m and only three from capture depths less than 30m.
The major finding from this study is that the mortality of snapper discarded from fish traps with capture depths of greater than 30m may be high. This mortality appears to be largely attributable to capture depth and rapid depressurization during capture. Rates of mortality of more than 20% are considered problematic (Muoneke and Childress, 1994), and∼45% of snapper from capture depths of greater than 30m died during the present study. Most of the NSW demersal trap fishery targets snapper in waters of greater than 50m (Ferrell and Sumpton, 1997) and, given that discard rates are currently in the order of 50% the mortality of these discards is of concern. Given that ∼66% of all recreationally caught snapper are also discarded (Henry and Lyle, 2003) it is likely that the mortality of recreationally caught and released snapper may also be an issue.
There is a current management initiative to increase the MLL of snapper in NSW from 30 to 32 cm, but the results presented here suggest that such an increase may not fully achieve the predicted increases in yield and egg production because of high rates of discard mortality.
It has been previously demonstrated that MLLs for snapper in New Zealand may not be effective in increasing stock size if discard mortality is high (Harley et al., 2000).
Gene R. Wilde
Wilde is professor of fishery ecology at the Department of Biological Sciences, Texas Tech University, Lubbock
17 studies that assessed the potential benefits of venting in 21 fish species and 1 composite group.
The effects of venting did vary with capture depth: venting was slightly beneficial to fish captured from shallow waters, but appeared to be increasingly harmful for fish captured from progressively deeper waters.
As a captured fish is brought to surface...gases may leave solution and form bubbles (emboli) in the blood, and various tissues and organs, including the eyes, brain, heart, arteries, gills, spleen, fins, musculature, and the dermis beneath the scales.
The Australian National Strategy for the Survival of Released Line Caught Fish recently endorsed venting as has, in effect, the U.S. National Marine Fisheries Service, which now requires offshore anglers in U.S. territorial waters in the Gulf of Mexico to have venting devices in their possession.
The available information provides virtually no support for the practice of venting as a means of increasing survival of captured and released fish. This result is consistent across a variety of experimental and field study protocols, within and among various species of fish, including species captured in freshwater and in saltwater, and from various depths.
Although fish that can swim away or submerge commonly are considered to have survived catch and release, this assumption is largely untested and there is some evidence that the ability to swim away is unrelated to survival. It is, perhaps, the counterintuitive nature of this result, along with some wishful thinking, that has perpetuated the practice of venting.
However, the physiological effects of barotrauma are not remediated simply by returning the fish to its capture depth (Morrissey et al. 2005) and many barotrauma injuries are unaffected by recompression
The available evidence fails to demonstrate that venting fishes exhibiting symptoms of barotrauma promotes post-release survival. In fact, it is possible that this practice decreases survival of fish captured from deeper waters, presumably because of the greater severity of their barotrauma symptoms. Venting fish should not only be discouraged by fishery management agencies, but given the possibility that venting adversely affects survival of released fish, this practice should be prohibited, rather than mandated.
I got half way through writing a response in a similar vein to Bazza’s
post, then initially chickened out, humanity looks at everything from a
perspective of how to utilize that resource for its benefit. If you looked at it from an ecological
perspective then the ranking of most harm would be:
- Fish caught and kept (removed from ecosystem)
- Fish caught, released and dies (this is not a full loss from the
ecosystem)
- Fish caught, released and survives
- No fish caught
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