Where is the Reticulated dragonet hiding? Is it in plain sight?

A tale of two fishes – Lisa Nihill, GMIT

Where is the Reticulated dragonet hiding? Is it in plain sight?

I learned to dive in the subtropics while travelling and got my Divemaster in the Andaman Islands. Having come from Dublin suburbia I was ignorant of the majestic beauty of our own oceans until I returned. I feel that the term “Divemaster” was not entirely deserved by me until I had completed my first season here. Wild swells, tidal currents of 6knots, wind, cold. All these tough conditions contribute to the high productivity supporting a diverse array of life here. When the dust settles and the visibility is good there is a world of colour which rivals coral reefs, and like our sunsets are never the same from day to day.

When identification comes down to small details in the field a combination of these conditions can really make life difficult. We are in their world, and we are certainly not as prepared for it as they are no matter how much gear is dangling off us. They are often very well camouflaged in their environment, you need to “get your eye in”. Still there are organisms I don’t see until they move (been inked before you’ve seen the cuttlefish?). Particularly when the viz is like this,

 Diver in poor visibility, turbid water. (Nguyen et al,2019)

another day you get this,

Me at Gurrig Island, Maharees. (Sarah Tallon, 2013)

Bottom dwelling (benthic) organisms like the dragonets are designed to go unseen. They cruise around on the bottom feeding on small crustaceans and worms, even starfish have been found in their stomachs. They in turn have been found in the stomachs of bigger fish including cod. The ICES fish stomach contents survey returns an incidence ratio of Callionymus lyra 10:1 Callionymus reticulatus. This ratio is closer to Seasearch data (7:1) and MarLiN Marine Survey data (professional) (7:1), interesting that these are so different to records from commercial surveys. Searching through papers for comprehensive surveys of dragonets I came across a paper written by Dr Paulin King, a study on C. lyra in Galway Bay, and as luck would have it one of my favourite lecturers. During the following interview we talked about C. reticulatus and I asked had she come across many of them during sampling, she said she had not (King et al, 1994).

This got me thinking again about their differences, back to the drawing board so to speak. Size could be an important factor here, the Common is the larger of the two max length male 30cm, Female 20cm. Pauline collected her samples from bycatch piles on Nephrops trawlers mostly in Galway Bay, the cod end would have a mesh size of about 80mm diamond mesh, although this size is being reviewed. In her paper she mentions the diversity amongst the destructive piles. I wonder now if the smaller size of the Reticulated makes it less susceptible to the trawl. Pauline found among her samples a significant deviation from 1:1, M: F, there were more males in the samples, and it was suggested this could be because of the difference in size between sexes. The Reticulated Male max. length is 11cm, Female 6.5cm. Could this be the reason? Let me know what you think? lisaihill@gmail.com g00363522@gmit.ie

References

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