Acoustic Telemetry of Fish

Introduction

Changes in trophic levels of fish landed by global fisheries have been evident over the last

50 years. Pauly et al., (1998) coined the phrase ‘Fishing down the food web’ to describe this

on-going trend. He explains how landings from global fisheries have shifted from mainly

large piscivorous fish to smaller invertebrates and planktivorous fish. A well-known example

of this is the decline of bluefin tuna, Thunnus thynnus in the Western Atlantic (Myers &

Worm, 2003). This species has been described by Safina, (1993) as being one of the most

vulnerable and over-exploited of creatures. When further investigated the decline of this

species can be explained by looking at how landings of this species has increased over the

years, as shown in catch records (Myers & Worm, 2003). As more fisheries look toward

lower trophic level species, the total catch from global fisheries keeps rising (Pauly et al.,

2000). With the continually added pressure on fish populations from humans, Ecosystem-

Based Fisheries Management (EBFM) have made ocean zoning, a scheme for dividing oceans

into sectors with a defined set of rules for managing each sector (Courtney & Wiggin, 2003),

a critical element of their protocol to establish what kind of human activity is sustainable

within each sector, considering both the geographical area the sector falls within and the

region of the world it occupies i.e. small area in the tropics or large area in Antarctica

(Pikitch et al., 2004). This leads us to ask the following questions; Why does all this matter?

Why is it important to study fish and recognise these trends? The main answer to these

questions is global fisheries management. It is important to control catch quotas and fishing

areas or else with continued over fishing, more and more large predatory fish and other fish

of high trophic levels could become depleted (Myers & Worm, 2003).

By studying life history traits of fish and the range of behaviours they exhibit, global fisheries

can be better managed. Understanding the movements of fish, both broad scale and fine

scale movements and being able to predict where certain species will be at different times

of the year and what size they are at that time can help set catch quotas and ensure fishing

is carried out in the most efficient and sustainable manner. This will also help to identify

important hotspots and migration routes. Sanchirico et al., (2006) explains how the

identification of these hotspots can promote the idea of a no-take zone in which fishing is

prohibited. This will allow the increase of conserving biodiversity and protecting sources of

larvae and biomass.

Understanding how the impacts of man have affected fish communities is also useful to

judge how conserved a certain species is. Historically, an example of how man has impacted

fish communities has been shown by the collapse of the Grand Banks in Canada. In a study

by Myers et al., (1997) they describe how six fisheries of Atlantic Cod, Gadus morhua all

collapsed within a time space of 4-6 years of each other leading to a ban on fishing between

1992-1993, but the population levels had become so low they were unable to recover.

Hutchings & Myers, (1995) proposed the reason for this was the advancement in fishing

technologies through the years. Fishing vessels are now equipped with bigger and stronger

nets, accompanied with sonar technology for finding where fish are (Misund et al., 1997;

Horne, 2000).

Historically, the movements of fish were recorded using simple methods such as mark and

recapture. This was a useful technique for answering simple questions such as does fish

population 1 move between site A and site B. A disadvantage of this method is that it can be

quite time consuming and it can be hard to recapture individuals which may limit the

accuracy of data interpretation (Hobson, 1999; Cunjack et al., 2005). Simple methods such

as mark and recapture can prove to be more useful that modern methods such as acoustic

telemetry depending on the study. Of all methods used to study fish movements and

behaviour, Time Depth Recorders (TDR’s) are the most widely used, not only on fish but

other shallow diving animals (Hays et al., 2007). Advances in technology have allowed for

different types of studies to be carried out than previously thought of, using other

techniques. Radio transmitters, TDR’s and archival loggers are examples of a more

technological approach to studying animal behaviour. These devices work on the basis of

sending data to a receiver or storing data on a type of medium (Cooke et al., 2004). In more

recent years acoustic telemetry has been used to describe fine scale movements of fish by

recording the acoustic signal sent from a fish fitted with a transmitter using a number of

different ‘active’ and ‘passive’ methods (Heupel & Hueter, 2001). Using this approach we

can build up an idea of residency patterns (Chapman et al., 2005), foraging ecology (Milne et

al., 2005) and resting areas (Johnson et al., 2009). Acoustic telemetry focuses more on the

movements and behaviour of individuals rather than populations, but when used with other

equipment such as sonar whole populations can be tracked. Also acoustic tracking can be

used hand in hand with mark and recapture methods. Individuals that are marked can also

be fitted with an acoustic transmitter and followed so that if they are not recaptured, it will

be evident where they did go. These are examples by which the two methods complement

each other, as shown in a study by Egil and Babcock, (2004) when they described how using

large-scale mark and recapture along with acoustic telemetry can be useful in estimating

fisheries yield enrichment within a marine reserve.

The use of acoustic telemetry can also be used to give an insight into questions that still

pose a subject of debate such as how different factors affect fish at both species and

population level. Changes in migration routes and times have been recorded over the last

decade and have shown a change in both aquatic and terrestrial animals and the reason can

often be attributed to climate change (Sims et al., 2001; Newson et al., 2008). These

changes can often be linked with other factors which occur as an indirect effect of climate

change such as the alteration of prey distributions, as seen changes in migration of bluefin

tuna shown by Walther et al., (2002).

This review aims to discuss how acoustic telemetry has been used to study fish movements

and from this, better understand certain behaviours such fine scale movements (foraging

ecology, residency patterns, species interaction) and broad scale movements (migration,

reproduction, geographical dispersion). In addition to this, understanding how

environmental influences can have an effect on the distribution can help improve

population assessments (Brill & Lutcavage, 2001).

Fine Scale Movements

These types of movement are described within a fine geographical resolution. Individuals

fitted with acoustic transmitters can provide insights into how life history traits differ

between species. Collecting data for fine scale movements can be achieved in a variety of

ways. Methods of ‘active’ and ‘passive’ tracking of marine fish have been described by

Johnston et al., (2009). Active tracking involves following a tagged fish from a distance in a

boat using receiving equipment tuned into the correct frequency, such as a directional

hydrophone and recording fixed GPS position as demonstrated in a study by Morrissey &

Gruber, (1993). Passive tracking involves an array of receivers dispersed within a geographic

range which records every time a tagged fish passes within its range as shown by Johnston

et al., (2009). To determine if a fish is in transient, foraging or resting we can consider

changes from the rate of travel it exhibits and attribute differences in behaviour. Block et

al., (1992) showed how using acoustic telemetry, depth and swimming speed of blue marlin,

Makaira nigricans could be recorded. They concluded that the individuals that were tagged

were not part of a resident group and were actually passing along a migratory route through

the islands of Hawaii. This study is an example of how acoustics can be used to study

residency patterns, species interactions and migration routes.

Movements within the home range of a fish can attribute to its fine scale movements. Home

range has been described as the relative frequency distribution of an animal over defined

geographic range in a given period of time (Seaman & Powell, 1996). By determining home

range we can obtain a more accurate definition of fine scale movements as it can be defined

differently between species. Heupel & Hueter, (2001) demonstrated how acoustic telemetry

can be used to record these behaviours during fine scale movements which supports

research carried out by Bolden, (2001) showing that acoustic telemetry can be used to

determine the home range of certain species of fish. Fine scale movements can be

attributed to foraging for food or reproductive activities, and not confusing this with a

passing species on a long migratory route. These movements can give an idea of areas of

high prey density, as shown by Josse et al., (1998) where by acoustic surveys in French

Polynesia showed the movements of two species of tuna and their prey.

Movements connected with reproduction may be observed at both fine and broad scales.

On a smaller scale, Flavelle, (2001) was able to identify fish that exhibited spawning habitat

selection through acoustic telemetry studies. Knowing this information can be crucial to the

survival of many species and play a major role in global fisheries management and

effectiveness of marine reserves (Rowley, 1994).

Broad Scale Movements

The use of acoustic telemetry has been quite limited when studying broad scale movements

as technological advances have moved more towards satellite tags, restricting acoustics to

short term tracking (Bruce et al., 2006). It can however help understand broad scale

movements taken by fish. By using acoustic telemetry, early ocean migration and where the

beginning of a migration route occurs can be recorded before moving to satellite tracking,

as shown in a study by Lacroix et al., (2004). Such data can be of great importance for

fisheries management of migratory species by defining migration patterns. As technology

has developed we can now track acoustically tagged fish for a period of up to one year

through the use of self-contained submersible receivers. This development shows how

autonomous acoustic tracking systems can give insights into the early and vulnerable life

history stages of juvenile fish (Welch et al., 2002).

Moving beyond home range, listening stations can be set in place over a broad spectrum

that a fish utilises. These types of studies can be useful when looking at reproductive areas,

which is closely related to early migration of juveniles as discussed before. Robichaud &

Rose, (2002) showed how acoustic telemetry can be used to depict behavioural differences

between males and females during spawning period. Differences in behaviour both pre- and

post-spawning have been identified in different species of fish. Acoustic studies have shown

how the degree of site fidelity changes between species. Humston et al., (2005) was able to

contradict previous studies of bonefish Albula vulpe and conclude that these fish did not

undertake extensive movements between different habitats but instead utilised shallow

habitats in the northern Florida Keys.

Species Interaction

As discussed in the previous section, acoustic telemetry can explore a number of different

types of behaviours, many of which conventional methods such as mark and recapture

cannot do. It is clear from previous studies that through tracking we can identify foraging

grounds (Dagorn et al., 1999), breeding and spawning grounds (Robichaud & Rose, 2002),

migration routes (Lacroix et al., 2004) and residency patterns (Collins et al., 2007). Bégout &

Lagardére, (1995) go on to show how through the use of acoustic telemetry, species interaction and

behavioural alteration can be observed. They showed that individuals that remained as part of a

school were generally more active and displayed a diurnal pattern, whereas individuals that

remained solitary were not as active and displayed nocturnal activity.

Conservation

Through studying behaviour of fish and using acoustic studies to see where they go and why, we can

help better conserve species. We can also help identify trends as to why some species are more in

decline than others and put in place legislation and quotas to help resolve this problem. Species

identification by acoustic telemetry is a long term goal aimed by fisheries and biologists. The

purpose of identifying fish by acoustic telemetry and not visually is to be able to increase the

amount of information collected through an increase in frequency bandwidth or number of acoustic

beams. In order to do this reliably, a set of statistical metrics that can discriminate between a wide

range of similar body shapes and sizes. When identifying species a number of factors need to be

considered. Position of fish in the water column and type of habitat it normally utilises can have an

effect on the accuracy of identification (Horne, 2000). Being able to identify fish species without

catching them or causing stress provides a much more efficient method of carrying out certain types

of research that require knowledge of where a fish is at a certain time as it will not alter their

behaviour.

To implement areas of conservation and no-take zones, various studies have been carried out to see

where certain species of fish go around their home range or place of capture. Chapman et al., (2005)

showed how two species of shark were caught and tagged with an acoustic transmitter, and when

released stayed within the proposed conservation zone. This study provided substantial evidence of

an area in which biodiversity can flourish if human activity is restricted. Klimley et al., (1988) further

showed how with the aid of acoustic telemetry, scalloped hammerhead sharks, Sphyrna lewini were

able to be tracked revealing that they aggregated close to a seamount during the day, then at night

moving separately into the surrounding pelagic areas. At dawn they all returned and remained at

the same seamount until the following night. This temporal pattern was related to the light-dark

cycle where individuals remained during the day and departed at night. The fact that these sharks

returned repeatedly to the tagging site provides evidence for any future proposals that this area be

considered as a no-take zone. In order to implement such areas, biologists need to have knowledge

of fish’s spatial ecology (Cooke et al., 2005). To aid the conservation of a species or number of

species, continuous knowledge of their ranges within their life span is essential and can be achieved

through continual tracking, as described by O’Dor et al., (1998).

Ocean Tracking Network

Ocean Tracking Network (OTN) comprises of hundreds of researchers from OTN’s 14 ocean regions,

together studying how marine life and climate are changing worldwide. Their range of study spreads

over all five of the world’s oceans. There were many reasons for setting up such a network, some of

which included the rapid decline in large pelagic fish such as bluefin tuna and blue marlin (Myers and

Worm, 2003; Polachec, 2005). With the use of acoustic telemetry combined with archival tags, OTN

has set up one of the world’s largest tracking networks, one which can sample 2000 times more

frequently and with ten times more accuracy and consistency, for example the Halifax Line. A recent

study undertaken in February of this year by the Commonwealth Scientific and Industrial

Research Organisation (CSIRO) tagged 230 juvenile southern bluefin tuna with acoustic

transmitters on the south coast of Australia. Using three OTN cross-shelf monitoring lines,

each fitted with 20 receivers, the seasonal movements of these juvenile fish were able to be

recorded over three years, indicating any change in response to climate change. The way in

which data are transmitted through OTN networks are unique. Acoustic receivers are place

within each other’s range. Once a tagged fish passes within a receivers range, the signal

picked up is able to be passed along other receivers until it reaches a listening station on

shore. This type of data transmission is referred to as a ‘Daisy-chain’ data flow. Underwater

fibre-optic cables can also relay data from a receiver to a listening station. Along with

transmitting a signal received from a passing fish, environmental sensors along the line relay

the physical state of the ocean at the time. From the results of past and present research

from OTN’s global network, it has been possible to help address climate change, ocean

modelling, and marine resource management.

Conclusion

To conclude, it has been shown that acoustic telemetry has evolved from simple methods of

sampling and tracking such as mark and recapture, leading to advances in technology such as

VEMCO V16 acoustic tags (http://www.vemco.com/pdf/v16cont.pdf) which can be used as simple

tag to show the location of an animal or they can be depth and temperature sensors. This has

opened a window to different types of questions to be answered. Although acoustic data have

proven to be extremely useful to fisheries management and migration studies as shown in previous

sections of this review, it still has some limitations. Active tracking requires a lot of manual labour

and can be very time consuming, when compared to other tracking methods such as satellite

tracking and passive tracking in which an array of listening stations are set up, methods of which are

demonstrated by OTN such as receivers attached to buoys and on the underside of ships. Acoustic

telemetry has opened doors into aspects of animal’s lives and evolutionary advances in this field are

becoming increasingly evident. One of the main objectives faced by producers of acoustic telemetry

products to produce a tag with the ability to identify species and record environmental data. Just as

acoustic tags are limited in this way, satellite tags are limited as the animals they are attached to

need to break the surface in order to transmit a signal. Future research and technology may lead to a

more complex range of tags, able to identify all these factors and identify more in depth information

regarding life history traits and behaviours related to species and by doing so, better manage global

fisheries and aid in conservation strategies.

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