Fishing - multispecies management approaches: evaluation

Discussion

Evaluation of multispecies management approaches

The evaluation of each of the management approaches against the performance indicators is summarised in Table 4.

For the ICES MSY approach, the sustainability indicators are all met in that the realised fishing mortalities and harvest rates do not exceed MSY values and SSBs all exceed MSY B_trigger values. However, catches for most stocks are lower than seen during the historical period due to the strictly implemented landing obligation exacerbating choking effects. The landing obligation enables the recovery of the cod stock which ultimately leads to higher catches of cod, and most other stocks, in the long term. Despite this, the multispecies yield of 0.71 indicates a substantial amount of foregone catch across all the stocks due to choking of the fleets, most commonly by cod, sole and whiting.

The choking effects can also be seen in the reductions in fleet fishing effort which are largest under this management approach. Similarly, fleet incomes were reduced although this was not felt equally across the fleets. For example, the TR1 fleet for vessels over 15 metres saw an increase in its share of the annual income due to the larger catches coming from the recovered cod stock. Conversely, the BT2 fleet and over 15 metre TR2 fleet took a smaller share of the income due to the landing obligation inducing stronger choking by plaice and Nephrops, respectively.

The CFP implementation of interspecies flexibility gave very similar results to the ICES MSY approach in terms of SSB, catches and fishing mortality. This suggests that this implementation does not offer enough flexibility to alleviate choking effects sufficiently to substantially increase catches. Nonetheless, this management approach saw stock biomasses and realised fishing mortalities remaining within sustainability limits.

At the fleet level, subtle differences were seen between the CFP interspecies flexibility approach and the ICES MSY approach. Individual fleets did not see their fishing effort or incomes reduced as much under this approach indicating that choking was somewhat alleviated by this scheme. However, this benefit was not felt equally across the fleets with some seeing smaller reductions in their income share compared to the ICES MSY approach. This suggests that this scheme allows only some fleets to more successfully alleviate choking to increase their catches.

The alternative implementation of interspecies flexibility resulted in greater differences compared to the ICES MSY approach. Catches under this approach were noticeably higher and SSBs were correspondingly lower. Furthermore, the realised fishing mortalities did exceed F_MSY values for some stocks although SSBs remained above MSY B_trigger values for all stocks. The multispecies yield value of 0.9 indicates less foregone catch under this approach: however, this was obtained by exceeding the TAC on some stocks, particularly non-target stocks. This is because this alternative approach allowed quota for non-target stocks to be used to cover over-quota catches of target stocks thereby driving fishing mortality upwards.

Table 4:

Performance of each management approach against performance indicators. The degree of shading indicates either good (no shading), moderate (light shading) or poor (dark shading) performance.

The quota points system gave broadly similar results to the ICES MSY approach and the interspecies flexibility approaches in that all stocks remained above their MSY B_trigger values and the realised fishing mortalities and harvest rates were broadly at or below their MSY values for most stocks. Additionally, all stocks were seen to recover above MSY B_trigger levels even though the catches of threatened stocks were not restricted explicitly. However, in contrast to the ICES MSY approach, the realised F exceeded F_MSY for haddock and the TACs were exceeded for haddock and whiting. This is reflected in the slightly higher multispecies yield of 0.76 for the quota points system approach.

Overall, catches were reduced most on flatfish under the quota points approach when compared to the historical period. Unlike the other management approaches, the quota points system implementation allowed a fleet’s effort share between areas to change to maximise the overall fleet effort. This resulted in some fleets shifting effort away from the North Sea (Subarea 4) towards the West of Scotland (Division 6.a) to avoid their choke stocks - namely flatfish and Nephrops - which were not represented in the model in this area. Although this effect is an artifact of the model setup, as well as being unrealistic, it shows the importance of avoidance behaviour to reduce the effect of choke stocks.

This change in métier effort share was predicated on maximising fleet fishing effort whereas maximising profit would be more realistic. In most cases, fleet effort was either maintained or increased over time though this did not necessarily translate into increased income. This is somewhat unrealistic as additional fishing comes with associated costs and will not be undertaken without it securing additional income. The affected fleets tended to be those that historically raised income from Nephrops or flatfish stocks. Therefore, the shift of effort towards the West of Scotland (Division 6.a) allowed them to continue fishing, maximising effort, but at the expense of their usual high value, target stocks. Overall, fleets targeting gadoid stocks benefited the most financially under this management approach.

The SFA Others pool approach performs differently over time against both sustainability and economic performance indicators. Gains in catches in the short term ultimately led to lower catches in the long-term from stocks with poor stock status. This management approach sees SSBs falling below the MSY B_trigger and/or B_lim reference points for several stocks. This is driven by the increase in catches across most of the fleets from using the unused quota in the Others pool to cover over-quota catches of target stocks. Therefore, the target fishing mortalities are generally exceeded, driving down SSB and lowering catches in the long term. The implementation of this scheme appears to be able to counter the action of the ICES harvest control rules to regulate fishing mortality.

Only select fleets saw increases in effort and income, particularly the Scottish TR1 over 15 metre fleet which saw its effort and income increase over time as it was able to catch more high-value, target stocks by counting over-quota catches against the pooled, unused quota from non-target stocks. This underlines the issue of choking as such a large volume of unused quota is available for the Others pool. Indeed, as the increased fishing mortality on target stocks degrades the stock status it alters the most common choke stocks across the fleets from being a mix of sole, whiting and cod to being cod and haddock. Ultimately, this reinforces the demand for an Others pool as a way to avoid being choked by cod and haddock.

Additionally, the SFA Others pool approach sees a decrease in catch diversity for half of the fleets whereas the other management approaches result in an increase in most fleets. It is the main gadoid, offshore trawlers that see an increase in catch diversity, mostly as the poor stock status of cod leads to lower catches of this stock and therefore a catch composition more equally distributed across the stocks. In contrast, the other management approaches see an increase in catch diversity across nearly all fleets due to stock recovery driving up catches across all stocks.

It should be noted that the SFA Others pool approach was specifically designed to alleviate the choking issues experienced by the offshore whitefish fleet. The initial increases in catch, effort and income seen for the TR1 over 15 metre fleet shows that it is does this successfully in the short term. Further refinement to the implementation of this approach (see next section) could be used to address the poor stock statuses seen in the long term under this scheme.

Limitations and recommendations

The performance on the multispecies management approaches shown here are limited by the way these approaches are implemented in the multispecies, multi-fleet model. Technical limitations on the way the interspecies approaches have been implemented here include the dependence on the definition of target and non-target stocks, the dependence of quota availability on the number of stocks included in the model and the assumption that fleets have perfect knowledge on how to use quota transfers to maximise catches.

The differences between the two interspecies flexibility implementations suggests that fewer restrictions on the type of quota transfers can reduce the amount of foregone catch. However, in this simulation, allowing the transfer of quota from non-target to target stocks simply increased each fleet’s catch on their target stocks, often over their quota, providing there were enough non-target stocks to cover it. Therefore, the ability of this approach to more adequately control fishing mortality on target stocks needs to be explored through testing additional restrictions. Examples of such restrictions beyond limiting the amount of quota that can be transferred include restricting specific conversions (e.g. conversions to cod quota are not allowed) and setting bespoke exchange rates (based on sale price, profit per tonne, stock health), to prevent low value quota being exchanged to high value quota.

A version of interspecies flexibility is used in Icelandic fisheries where the scheme is designed to account for unavoidable over-quota catch of certain species rather than allow unrestricted exchange of quota from one species to another. The scheme uses specified exchange rates based on units of "cod equivalents" (CE) which are relative to the species’ market value. It also employs additional flexibilities such as quota trading and banking or borrowing quota between years (Christensen et al. 2009). An evaluation of this Icelandic fisheries scheme found that when the profitability of a species is artificially inflated, it becomes more likely that its total catch will be above its TAC as quota is transferred to cover the over-quota catch (Woods et al. 2015). In reality, the Icelandic system is more balanced due to various reasons including the high profitability of cod, the restriction on converting other species to cod quota, the low profitability of low abundance species and a diversity of interest and fishing practices across vessels.

Further exploration of the quota points system should consider maximisation of profit instead of effort and include more stocks, especially those located outside of the North Sea (Subarea 4). Moreover, alternative methods to derive the quota points total and the tariff should be explored and could also consider variations through time and space so that specific stocks are made more expensive during spawning time and in nursery areas or can vary between ICES areas. Then again, multiple tariffs could lead to an overly complicated system and may encourage misreporting of catches both spatially and temporally, especially if changes in costs were fairly abrupt between areas or time periods.

If this scheme were to be implemented then one advantage is that it would be relatively simple to add other regulations such as effort limitation, gear regulations and real time closures (Needle 2012). In addition, this scheme gives fishers greater flexibility regarding which stocks to spend their quota points on without the need to first obtain additional single species quota from elsewhere.

A key drawback of the model implementation of the SFA Others pool approach is that the size of the Others pool is limited by the number of stocks included in the model as well as the definitions used to identify non-target stocks. Additionally, further exploration is recommended to improve the performance of this approach in terms of the biological health of the stocks. Examples could include establishing suitable limits on the maximum size of the Others quota pool and on the maximum amount of single species quota that can be transferred.

Finally, the model results presented here were generated from one simulation replicate whereas, "best practice" for management strategy evaluation involves using thousands of replicates to adequately capture variability in stock biology and fleet behaviour. Several simplifications made in the model would also need consideration when evaluating the schemes further. Firstly, the implementations assume fleets have "perfect knowledge" on the best way to optimise their quota transfers or effort share. Secondly, the implementations also assume no change in targeting behaviour or catch efficiency in response to TAC changes year to year. Thirdly, the schemes are implemented to maximise either fleet effort or catches and do not consider the financial viability of this course of action. These three considerations would all affect the relative success or failure of the management approaches in reality.