Heat versus gill nets

There has been much talk about poor catches on the Daly River this year, following a disastrous wet season.

Before blaming gill nets, fishermen should first look at catch trends from the Barra Nationals and Barramundi Classic competitions (shown above).

Rainfall and barra catch is closely aligned, and is likely to remain so.

What concerns the author more than the effect of gill nets is the effect of continued warming of the climate. Before you dismiss this, please go to the bottom of the page and use the interactive graphic.

As we know, barramundi live in an extreme environment at the best of times. Large numbers of fish die, usually in the Build-up, after rain, when waterholes become superheated and organic debris quickly rots, causing oxygen levels to plummet.

Heat is now affecting tidal waters. In the shallow Gulf of Carpentaria, there have been die-offs of hundreds of hectares of mangroves, which is prime barramundi habitat.

Coral die-off has been well publicised in overheated tropical waters.

In my view, rising temperatures are a bigger threat to barramundi stocks than gill nets.

Overheated tidal shallows and floodplains, and overheated or even dry waterholes, will damage bait cycles, if not kill barramundi outright.

If you are in any doubt about temperature trends, look at the interactive graphic below, by Climate Central. It shows hot and cold temperature records from US cities. Use the pulldown to see cities across America, and note the trend in the past 20 years.

I don’t have a similar graphic for Australia, but no doubt the changes are similar.

If the heat trend of the past 20 years continues, we’ll be lucky to have barramundi some time in the future. Only recently a USA fisheries scientist said she was recording temperatures in salmon rivers that were not expected until 2070.

Which brings us back to barramundi gill netting. If there is a case for reducing netting, global warming is it.

Fish stocks will become more fragile as it gets hotter, and harvesting may have to be reduced, or stopped, to increase the chances of survival, and, with luck, adaption.

Also check out this FFF thread.

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