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NSW slot limits


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13 hours ago, Daryl McPhee said:

Mid-sized females (45 cm - 69 cm TL) dominate the production of eggs due to their abundance in the spawning aggregation

This would be right in the slot limit - So am i reading this extract right that the science doesn't quite back up the slot limits? With older / larger Female Flatties not really in the spawning aggregation?

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19 hours ago, Daryl McPhee said:

Here is a summary some published information from a colleague Dr Barry Pollock. 

The annual spawning aggregation of dusky flathead 'Platycephalus fuscus' at Jumpinpin, Queensland

Dusky flathead 'Platycephalus fuscus' form seasonal spawning aggregations where estuaries meet the ocean in eastern Australia. The present study at Jumpinpin in south Queensland shows that dusky flathead have a protracted spawning period with serial spawning during summer (November to April). They are rudimentary hermaphrodites with sex determined at an early juvenile stage. Sex ratios are skewed with males most common in the smaller size-classes (< 50 cm TL). Mid-sized females (45 cm - 69 cm TL) dominate the production of eggs due to their abundance in the spawning aggregation. Within the female component of the spawning aggregation, the occurrence of individuals exceeding the current maximum size limit of 75 cm TL is low (2.6%). Parasitic nematodes (philometrids) occurred in 8% of ovaries. Degenerated ovaries, in which atretic oocytes are common, are present in half of the very large females (70 cm - 75cm TL) examined. The current minimum size restriction of 40 cm TL for dusky flathead provides protection for 73% of males and 15% of females within the spawning aggregation. 

Bloody legend Dazza. Thanks

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It’s a power in numbers thing Hweebe. There’s way more sub 70cm female flatties in the breeding population so their egg production far outweighs the 70cm+. The paper also suggests that of the 75cm+ fish captured at the pin during the study, ~half had parasitic infections or atretic ovaries (ie not working). Some would argue that this doesn’t matter as half do not have parasitic infections and do have working ovaries but that’s just my opinion. 
 

I have a few problems with this study. The author has openly called for the upper size limit for flathead in Qld to be removed; he was/is also a reviewer and editor of the journal this was published in; and the sampling was focussed on one area of the flathead population using line fishing methods only. For an accurate investigation you would need to sample the population over the entire Qld coast over many years by methods independent of the recreational fishery. So overall in my opinion this is an interesting study on flathead at the Pin whose results cannot be applied over the greater Qld area. 
 

Slot limits may be used to protect certain parts of fish population (ie big Barra) biologically but may also be a reflection of fisher behaviour (eg fishers considering big flathead too precious to keep/kill). I think in this case the slot limit does both, but maybe reflects existing/changing attitudes around keeping big fish. 

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29 minutes ago, Andrew_P said:

Slot limits may be used to protect certain parts of fish population (ie big Barra) biologically but may also be a reflection of fisher behaviour (eg fishers considering big flathead too precious to keep/kill)

I’m good with this, as I think everyone on this forum would be. It also means future generations can also enjoy the thrills of catching and releasing a large specimen or devastation of getting busted off by a freight train.

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There is some work specifically in NSW. This is not work that I have been associated with, but the Abstract is below and the full text can be accessed here: Oogenesis, Oocyte Atresia, Ovarian Development and Reproductive Senescence in the Dusky Flathead Platycephalus fuscus (Teleostei) (escientificpublishers.com)

Abstract
The aim of the present study is to examine developmental changes of oocytes and ovaries of a wild population of dusky flathead Platycephalus fuscus (Cuvier, 1829). This fish is endemic to the east coast of Australia where it inhabits estuaries and coastal waters. It is extensively fished throughout its range. It is a serial spawning teleost, capable of producing vast numbers of externally fertilised eggs in batches over a protracted annual spawning period. Successful egg production, as indicated by the presence of hydrated oocytes and post ovulatory follicles, is commonly observed in small and mid-size females (35cm–65cm Total Length; 2-6 years old) which numerically dominate the female component of the spawning aggregation. Oocyte atresia, at various levels, commences at the vitellogenic oocyte stage, and occurs in all mature fish during the spawning period. Mass oocyte atresia and degenerate ovaries were commonly observed in large fish (>70 cm Total Length and 7 years old), indicating that reproductive senescence occurs after females reach this size.

 

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So whilst the >70cm specimens may have reproductive issues and they are not good for eating, the slot limit then really serves the purpose of allowing >70cm fish to grow to the size of the trophy / bucket list list 3m flattery size 🙂

 

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