FITZROY RIVER KING THREADFIN END OF SEASON REVIEW 2017

There were 9 forecasts made for King Threadfin in size of fish, catch rates, trends in stocks and recruitment. Catch details are based on T20 fishers that are the top 20% of fishers that catch 80% of the fish. Their catch rates do not reflect the catch rates of the total fishing population however their catches are more sensitive to changes in fish stocks and are comparable from year to year. Forecasts are available at www.crystal-bowl.com.au.

Season 2017 forecasts versus actual – end year review

T20 Fishers

Forecasts for King Threadfin have a moderate level of accuracy due to the limited data available so there is a greater range in the forecasts.
  • Of the forecasts for T20 fishers 8 were within the forecast range or revised range with 1 within 10% of the forecast range
  • There were 523 fisher days for 289 fish caught
  • The overall catch rate was 0.55 fish/fisher/day while for legal fish was 0.45 fish/fisher/day and was 44.5% lower than in 2016
  • The catch rates for 2017 are down compared with 2016 as much of the fishing effort was directed at Barramundi and the flow in Jan, flood in Apr and flow in Oct impacted on the catch of Threadfin, particular in the upper reaches of the river
  • Poor recruitment in 2016 has contributed to the drop in the overall catch rate
  • The average length of fish continues to rise and is 793mm in 2017, is 15.8% higher than in 2016 and the highest in 10 years
  • Trophy fish over 1m are 9.3% of the catch and that is the highest in 10 years
  • Legal fish kept were 25% of the fish that could legally be kept however that figure is an underestimate due to the high representation of taggers in the T20 fishers
  • Moderate flow in Jan, flooding in Apr and moderate flow in Oct has also impacted on the numbers of fish tagged
  • Forecast was for poor/moderate recruitment and was assessed as poor

Rocky Barra Bounty

  • In the Bounty there were 540 fisher days with 202 fish caught
  • There were 50 trophy fish which was 24.8% of the catch and a record for any Bounty

Environmental conditions

  • There was a moderate flow (0.35GL) in the river in Jan 2017, a major flood (4.84GL) in Apr 2017 and another moderate flow (0.19GL) in Oct

Infofish Australia
January 2018

MEASURE FORECAST

ACTUAL

GRAPH

FITZROY 2017

JUNE 2017

T20 fishers
Bounty fishers
Days fished
2008-2017
New measure
 
T20 fishers Days
158 523
Bounty Days
180 540
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Fish sizes
Trophy fish >1m
Legal - trophy fish 600-999mm

Undersize fish 200-599mm
 
5% (0-15%)
65% (55-75%)
30% (20-40%)
T20 fishers Bounty
9.3% 24.8%
72.7% 63.4%
18.0% 11.9%
T20 in range
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Percentage of fish in size ranges
2008-2017


Highest Lowest
LEGAL-TROPHY
2015 2009
73.7 3.6%
TROPHY
2017 2010
18.2 0.0%
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Average length of fish 2008-2017

Highest Lowest
Legal
2017 2008
793mm 443mm
Increase 15.8%
from 2016-2017
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Percentage of legal fish kept
T20 fishers
New measure

-

Kept
25%
(underestimate due to tagger representation in T20 fishers)
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Actual catch rates
T20 fishers
Fish/fisher/day
Revised Jun 17
T20 fishers
Overall
1.1 (0.9-1.3)
0.7 (0.4-1.0)
Legal fish
0.9 (0.7-1.1)
0.6 (0.3-0.9)
T20 fishers
Overall
0.55
In range
Legal fish
0.45
In range
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Catch rates percentage change compared with 2016
Revised Jun 17
Taggers
Overall
-20 - +20%
-30 - -70%
Legal fish
-10 - +30%
-40 - -80%
Taggers
Overall
-51.0%
In range
Legal fish
-44.5%
In range
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Catch rates by month
2015-2017
T20 fishers
Fish/fisher/day

New measure
Highest Lowest
Overall
Jan 2016 Nov 2015
3.2 0.1
Highest Lowest
Legal
Jan 2016 Nov 2015
2.3 0.0
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Actual catch rates taggers and avid fishers
Fish/fisher/day
2008-2017
Highest Lowest
All
2016 2010
1.13 0.04
Highest Lowest
Legal
2016 2010
0.82 0.02
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King Threadfin tags in river indicator of trends in stock
Most likely and range
2008-2017
Revised Jun 2017
Tagged fish 2017
(Jan-Dec)
400 (300-500)
200 (100-300)
Tagged fish 2017
(Jan-Dec)
328
Within original forecast range
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Recruitment
Tagged fish each year
Year 1 <300mm
Year 2 >=300-<500mm
Year 3 >=500-<600
Flow Dec-Mar
100,000ML
Poor/moderate
2017
Poor
(Incomplete data for 2016 and 2017)
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Commercial catchGrids R29 and R30
Catch tonnes
Catch rate kg/day
None forecast as river is now a net free zone Catch
2015
56.14t
Catch rate
59.9kg/day
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River flow and King Threadfin 2015-2017 FLOODS
Mar 2015
Apr 2017
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River flow and King Threadfin 2008-2017 Floods
2008
2011
2013
2015
2017
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DATA SOURCES

Data used in the Fitzroy Barramundi Crystal Bowl are:

BASIS FOR ANALYSES

In 2017 saltwater tidal maps (FRR, PAR, CIS) and freshwater maps (RAG, FRF) were separated so that data could be analysed for the different habitats. The analyses of the data were based on the following:

  • Effort data for taggers/avid fishers were the number of days fished in map areas FRR, PAR and CIS where King Threadfin and/or Barramundi were caught
  • Catch rates for taggers was calculated as fish/fisher/day
  • Catch rates for commercial fishers was calculated as kg/day
  • Stock trends were based on a modeled estimate of the number of tags in the river each year where the tag reduction rate was calculated based on the reduction of recaptures each year
  • The most likely number of tags was based on a tag reduction rate of 0.7 each year up to 2015 and 0.6 for 2016 taking into account no commercial catch
  • Recruits were based on tracking recruits over the first 3 years with fish in year 1 = 0-299mm, year 2 = 300-499mm and year 3 = 500-600mm so recruits for 2016 and 2017 are incomplete