FITZROY RIVER KING THREADFIN MID SEASON REVIEW 2017

There were 9 forecasts made for King Threadfin in size of fish, catch rates, trends in stocks and recruitment. Tagger/avid fisher catch rates do not reflect the catch rates of the total fishing population however as they are in the top 20% of fishers that catch most fish and their catches are more sensitive to changes in fish stocks and are comparable from year to year. Forecasts versus actual are available from www.crystal-bowl.com.au.

Season 2017 forecasts versus actual – mid-season June 2017 review

Taggers/Avids

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 taggers/avids 4 (45%) are within the forecast range or within 10% of the forecast range and forecasts remain unchanged
  • The catch rates for 2017 are down significantly compared with 2016 as most of the fishing effort has been directed at Barramundi and the flow in Jan and flood in Apr have made fish harder to locate
  • Catch rates have been revised based on current and expected conditions
  • Poor recruitment in 2016 has contributed to the drop in the overall catch rate compared to 2016
  • The catch rate for legal fish is 0.3 fish/fisher/day and is 63.5% lower than in 2016
  • The average length of fish continues to rise and is 718mm in 2017 and the highest in 10 years
  • Trophy fish over 1m are 17.3% of the catch and that is the highest in 10 years
  • Moderate flow in Jan and flooding in Apr has also impacted on the numbers of fish tagged
  • Forecast was for poor/moderate recruitment with early recruits recorded in Jan however there are insufficient data to make an assessment

Rocky Barra Bounty

  • Forecasts for the Bounty will be made in Sep due to the uncertainty from flooding in the river in Apr

Environmental conditions

  • There was a moderate flow in the river in Jan 2017 and then a major flood in Apr 2017
  • Climate outlook is for neutral conditions through to Feb 2018
  • Rainfall forecasts are only available for 3 months and the forecast is for a 45-55% chance of exceeding median rainfall from Jun-Aug

Infofish Australia
June 2017

MEASURE FORECAST

ACTUAL

GRAPH

FITZROY 2017

JUNE 2017

Fish sizes
Undersize fish 200-599mm
Legal - trophy fish 600-999mm
Trophy fish >1m


30% (20-40%)
65% (55-75%)
5% (0-15%)

Taggers/Avids
27.6%
55.1%
17.3%

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Percentage of fish in size ranges
2008-2017

Highest  Lowest
LEGAL-TROPHY
2015    2009
72.2    2.5

TROPHY
2017    2010
17.3    0.0

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Average length of fish 2008-2017

Fish/tagger/day
 

Highest   Lowest
2017   2009
718mm   443mm
increase 3.2% from 2016-2017

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Actual catch rates taggers and avid fishers
Fish/fisher/day
Revised

Taggers/Avids

Overall
1.1 (0.9-1.3)
0.7 (0.4-1.0)
Legal fish
0.9 (0.4-1.1)
0.6 (0.3-0.9)

Taggers/Avids

Overall
0.5
Legal fish
0.3

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Catch rates percentage change compared with 2016
Revised

Taggers/avids

Overall
-20% - +20%
-30% - -70%
Legal fish
-10% - +30%
-40% - -80%

Taggers/avids

Overall
-59.9%
Legal fish
-63.5%

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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
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
Tagged fish 2017 (Jan-Dec)
400 (300-500)
200 (100-300)
Tagged fish 2017 (Jan-Jun)
55
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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
Some early evidence of recruitment in 2017
(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 2017
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River flow and King Threadfin 2007-2016 Floods
2008
2011
2013
2015
2017
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Climate outlook to Feb 2018 BOM NINO34 Neutral conditions through to Feb 2018
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Rainfall Outlook BOM forecast 45-55% chance of exceeding median rainfall
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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 2015 and 2016 are incomplete