Hook Timer Manuscript

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Trot lines have historically been used by commercial and recreational

fisherman to target catfish and have also been used by biologists as a

management tool to monitor and evaluate catfish populations.

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However, trot lines have recently proven to be an effective method for collecting

Scaphirhynchus species, including the federally endangered pallid sturgeon.

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For example, since the inception of the Pallid Sturgeon Population Assessment Program in

2003 – the Nebraska Game and Parks Commission has collected almost 1,500 pallid sturgeon

with 1,100 being collected on trot lines within the last four years.

This collection technique has improved detection rates which has provided

information on survival estimates and population estimates for pallid sturgeon

and has been useful for targeting mature adult pallid sturgeon used for

telemetry studies and for the artificial propagation program.

So, trying to get a better understanding of fish / gear interaction and searching for other

examples where trot lines are used as a fisheries management tool, we found this article.

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The authors used a timing devise on their long lines to measure individual

capture times. This assisted long line fisherman to target optimal deployment

times (based on time of day), depths, habitats, and temperatures as their lines

sink to a predetermined depth and have also provided information useful to

determine feeding times of targeted species, reduce target species mortalities

from sharks, and increase capture efficiency through identifying optimal soak

duration.

However, there is no published study reporting the use of this timing devises

for freshwater fishes.

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So a simple Google search and we discovered a company in Florida that makes all types of

equipment for long line fishing including these digital timers.

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These LP Hook Timer are digital timers incased in a water tight plastic housing

and is powered by a double A battery.

The timer is activated by removing the magnetic plug which triggers the timer

and records time up to 24 hours.

For example, the timer on the bottom was activated 17 minutes ago.

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However, we had a couple preliminary concerns –

They’re big --- at just over 5” long and about 2.5” wide, we were concerned the overall size

could deter fish from striking the hook.

Also, since they are designed for marine fishing the present release weight is 8 to 10 pounds.

We knew our “small” freshwater fish couldn’t activate the timer with that release weight;

therefore, we had the release weight adjusted by milling the O-ring groove and fitting with a

smaller O-ring. This adjustment reduced the release weight to approximately 1.5 to 2 lbs.

This was the lightest we could go without the plug fall out during deployment.

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Because of those concerns and the overall price of each timer, we purchased

enough hook timers for 1 trot line plus a couple extras to conducted a

preliminary study to ---

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During our fall 2010 pallid sturgeon population assessment sampling, we

randomly selected eight Missouri River bends along the Nebraska / Iowa

boarder.

On each bend, we deployment 8 standard (non-hook timer) lines and 1 trot

lines rigged with hook timers

with both line types were fished in similar habitats -- on the inside bend within

the wing dike structures.

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So the preliminary results indicate catch rates for pallid sturgeon between

standard and hook timer trotlines were similar

and was actually slightly higher on hook timer trotlines (6.00) vs. STD lines

(4.2) for shovelnose sturgeon.

All other species were collected a low numbers.

Overall, the CPUE between our standard trotlines and hook timer trotlines

didn’t significantly differ.

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Looking at the activation rate objective ---- Overall 60 fish were collected on

our 8 trot line hook timer deployments with an overall activation rate of 68%.

Shovelnose sturgeon was the primary fish species collected and their

activation rates was slightly higher then the mean with a 71% activation rate

while only 1 of 4 pallid sturgeon activated the hook timer during this preliminary

study.

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Our final concern were the durability of these hook timers. In approximately

320 deployments, roughly 8 deployments per hook timer,

we had --- READ BULLETS

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After the preliminary study, we concluded that hook timers are a good gear to

aid us in understand the trotline / fish interaction.

So we purchased several more hook timers and the objective of this larger-

scale study was to ---

READ SLIDE

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Sampling occurred during our annual effort to collect reproductively ready

pallid sturgeon for the propagation program in early-April.

The study area was a 50 river mile reach of the upper channelized Missouri

River from the confluence of the Missouri and Platte rivers to just south of the

Iowa / Missouri state line.

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4 crews fish daily and deployed 8 standard trot lines and 2 hook timer trot lines

daily.

And similar to the preliminary study, all trot lines to deployed on the inside

bend between wing dikes.

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Overall, we deployed 100 trot lines rigged with hook timers resulting in 4,000

hook nights.

We collected over 1,400 fish with shovelnose sturgeon being the primary

species collected, follow by pallid sturgeon and a few channel catfish.

This resulted in an overall hook timer activation rate of 57% just slightly lower

then our preliminary study results.

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So we wanted to analyze if the lower activation rate was caused by smaller

fish that were unable to pull the hook timer plug.

Mean fork length for pallid sturgeon was significantly different for fish the did

and did not activate the hook timers.

However, shovelnose sturgeon fork length was not significantly different

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An addition to the 1,400 fish collected – we retrieved 307 hook timers that

were activated but didn’t collect a fish.

Therefore, we made the assumption that these where fish that escaped the

hook prior to be retrieved because the bait was missing and the timer was

activated.

Therefore, we can concluded - our trotlines had an estimated retention rate of

72.5%.

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The overall CPUE for sturgeon species was 14 fish per line and was primarily

shovelnose sturgeon.

With an overall total CPUE of 14.6 fish per line.

HOWEVER, when we accounted for the lost fish on the activated hook timers,

our CPUE extrapolates to 17.7 fish per line.

This is still probably underestimated because we don’t know the escapement

rate of fish from hooks where the hook timers were not activated.

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So next, we investigated the rate at which fish are collected on trot lines post

deployment.

Here the X-axis is the duration the trot line was fishing or deployed

And the Y-axis is the number of hook timers activated that retained a fish.

Are data indicates that --

21% of fish are collected in the 1st hour

34% of fish are collected in the first 2 hrs.

And over half --- 55% of fish are collected in the first 4 hrs.

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This is the same as the previous slide with the open dots being the number of

fish collected

However, the solid dots are the number of fish lost.

Lost fish mimics the distribution of fish that were retained. Therefore, we

concluded that fish escapement is not affect by hook duration.

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The next several slide are going to look at CPUE for our two sturgeon species.

The Y-axis that CPUE is based on hook availability.

For example, when we first deploy the line the number of hook available are

40; however, when a fish is caught the number of hook available is reduced to

39 and so on so it’s a real-time adjusting effort -----

When we look specifically at pallid sturgeon CPUE by hour. The highest

CPUE is the first hour post deployment, followed by the 3rd to 4th hour.

Overall, 21 of 31 pallid sturgeon collected with this gear were collected in the

first four hours.

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And shovelnose sturgeon follows this same trend as pallid sturgeon with the

majority collected the first hours and then declines throughout the soak time.

Overall, 62% of shovelnose sturgeon are collected within the first 5 hours post

deployment.

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For the next couple slides the Y-axis is the same --- However the x-axis is now

the actual time of day the fish were collected.

The highest CPUE for pallid sturgeon was observed between 1500 and 1600

hrs, followed by 1700 to 1800 hrs.

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And the shovelnose sturgeon data shows a similar pattern to pallid sturgeon

with the 1500 to 1600 hrs resulting in the highest CPUE.

There appears to be a peak in CPUE for both sturgeon species during that

time frame but it is just an artifact of when the majority of the gear was being

deployed during our 12 day intensive effort.

We also had a theory that fish feeding would increase around sunset / sunrise;

however, there appears to be little influence during these times.

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Finally, we wanted to investigate if pallid sturgeon were collected at different

frequencies based on origin –

Of the 58 pallid sturgeon collected only 31 activated the hook timers.

8 were genetically determine to be wild origin while the remaining 23 were

from hatchery stock.

It appears that origin didn’t affected collection rates.

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Of the fish that were transferred to the hatchery for reproductive assessment

5 were females and 6 were males

Again – collection times overlapped and it doesn’t appear there are any

differences.

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Reproductive and non-reproductive fish, also didn’t display any separation in

collection times.

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